Editing PDF

{{Short description|Portable Document Format, a digital file format}}
{{Other uses}}
{{pp-pc}}
{{Use American English|date=January 2023}}
{{Use mdy dates|date=January 2023}}
{{Infobox file format
| name          = Portable Document Format
| icon          = PDF_file_icon.svg
| icon_size     = 121px
| iconcaption   = Adobe PDF icon
| screenshot    = 
| extension     = <code>.pdf</code>
| _noextcode    = no
| mime          = {{Plainlist|
* <code>application/pdf</code>,<ref name="rfc8118">{{Cite IETF |title=The application/pdf Media Type |rfc=8118 |sectionname= |section= |page= |last1=Hardy|first1=M.|last2=Masinter|first2=L.|last3=Markovic|first3=D.|last4=Johnson|first4=D.|last5=Bailey|first5=M.|date=March 2017|publisher=[[Internet Engineering Task Force|IETF]]|doi=10.17487/RFC8118 }}</ref>
* <code>application/x-pdf</code>
* <code>application/x-bzpdf</code>
* <code>application/x-gzpdf</code>
 }}
| _nomimecode   = true
| uniform type  = com.adobe.pdf
| magic         = <code>%PDF</code>
| owner         = [[Adobe Inc.]] (1991–2008)<br />
[[ISO]] (2008–)
| genre         = 
| released      = {{Start date and age|1993|6|15}}
| latest release version = 2.0
| latest release date = <!-- {{Start date and age|YYYY|mm|dd}} -->
| container for = 
| contained by  = 
| extended from = 
| extended to   = [[PDF/A]], [[PDF/E]], [[PDF/UA]], [[PDF/VT]], [[PDF/X]]
| standard      = ISO 32000-2
| open          = Yes
| url           = {{URL|https://iso.org/standard/75839.html}}
| image         = 
| typecode      = <code>PDF </code><ref name="rfc8118" /> (including a single trailing space)
}}

'''Portable Document Format''' ('''PDF'''), standardized as '''ISO 32000''', is a [[file format]] developed by [[Adobe Inc.|Adobe]] in 1992 to present [[document]]s, including text formatting and images, in a manner independent of [[application software]], [[Computer hardware|hardware]], and [[operating system]]s.<ref name="pdf-ref-1.7">{{cite web|author=Adobe Systems Incorporated|url=https://www.adobe.com/devnet/acrobat/pdfs/pdf_reference_1-7.pdf|title=PDF Reference|date=November 2006|edition=6th|version=1.7|url-status=dead|archiveurl=https://web.archive.org/web/20081001170454/https://www.adobe.com/devnet/acrobat/pdfs/pdf_reference_1-7.pdf|archivedate=October 1, 2008|accessdate=January 12, 2023}}</ref><ref>{{Cite web|last=Warnock|first=J.|url=https://www.pdfa.org/norm-refs/warnock_camelot.pdf|title=The Camelot Project|date=14 October 2004<!--dates from PDF source-->|orig-date=Original date 5 May 1995|archive-url=https://web.archive.org/web/20110718230852/http://www.planetpdf.com/planetpdf/pdfs/warnock_camelot.pdf|archive-date=July 18, 2011|url-status=live}}</ref> Based on the [[PostScript]] language, each PDF file encapsulates a complete description of a fixed-layout flat document, including the text, [[font]]s, [[vector graphics]], [[raster images]] and other information needed to display it. PDF has its roots in "The Camelot Project" initiated by Adobe co-founder [[John Warnock]] in 1991.<ref>{{Cite web|title=What is a PDF? Portable Document Format {{!}} Adobe Acrobat DC|url=https://www.adobe.com/acrobat/about-adobe-pdf.html|access-date=January 12, 2023|publisher=Adobe Systems Inc.|language=en|archive-date=January 30, 2023|archive-url=https://web.archive.org/web/20230130032548/https://www.adobe.com/acrobat/about-adobe-pdf.html|url-status=live}}</ref>
PDF was standardized as ISO 32000 in 2008.<ref>{{cite web |url = http://wwwimages.adobe.com/www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf |title = ISO 32000-1:2008 |archive-url=https://web.archive.org/web/20180726064724/http://wwwimages.adobe.com/www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf | archive-date=July 26, 2018|url-status=dead}}</ref> The last edition as ISO 32000-2:2020 was published in December 2020.

PDF files may contain a variety of content besides flat text and graphics including logical structuring elements, interactive elements such as annotations and form-fields, layers, [[rich media]] (including video content), three-dimensional objects using [[U3D]] or [[PRC (file format)|PRC]], and various other [[File format|data formats]]. The PDF specification also provides for encryption and [[digital signature]]s, file attachments, and [[metadata]] to enable [[workflow]]s requiring these features.

== History ==
{{Main|History of PDF}}

The development of PDF began in 1991 when [[John Warnock]] wrote a paper for a project then code-named Camelot, in which he proposed the creation of a simplified version of PostScript called Interchange PostScript (IPS).<ref name="Pfiffner_Page_137">{{cite book |last1=Pfiffner |first1=Pamela |title=Inside the Publishing Revolution: The Adobe Story |date=2003 |publisher=Peachpit Press |location=Berkeley |isbn=0-321-11564-3 |page=137}}</ref> Unlike traditional PostScript, which was tightly focused on rendering [[print job]]s to output devices, IPS would be optimized for displaying pages to any screen and any platform.<ref name="Pfiffner_Page_137" />

[[Adobe Systems]] made the PDF specification available free of charge in 1993. In the early years PDF was popular mainly in [[desktop publishing]] workflows, and competed with several other formats, including [[DjVu]], [[Envoy (WordPerfect)|Envoy]], Common Ground Digital Paper, Farallon Replica and even Adobe's own PostScript format.

PDF was a [[proprietary format]] controlled by Adobe until it was released as an [[open standard]] on July 1, 2008, and published by the [[International Organization for Standardization]] as ISO 32000-1:2008,<ref name="iso-standard">{{cite web |url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=51502 |title=ISO 32000-1:2008 – Document management – Portable document format – Part 1: PDF 1.7 |publisher=ISO |date=July 1, 2008 |access-date=February 21, 2010 |archive-date=December 6, 2010 |archive-url=https://web.archive.org/web/20101206175751/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=51502 |url-status=live }}</ref><ref>{{cite web |last=Orion |first=Egan |title = PDF 1.7 is approved as ISO 32000 | work =[[The Inquirer]] |date=December 5, 2007 
|url = http://www.theinquirer.net/gb/inquirer/news/2007/12/05/pdf-approved-iso-32000 |access-date=December 5, 2007 |url-status=dead|archive-url = https://web.archive.org/web/20071213004627/http://www.theinquirer.net/gb/inquirer/news/2007/12/05/pdf-approved-iso-32000 |archive-date=December 13, 2007}}</ref> at which time control of the specification passed to an ISO Committee of volunteer industry experts. In 2008, Adobe published a Public Patent License to ISO 32000-1 granting [[royalty-free]] rights for all patents owned by Adobe necessary to make, use, sell, and distribute PDF-compliant implementations.<ref>{{cite web|url = https://www.adobe.com/pdf/pdfs/ISO32000-1PublicPatentLicense.pdf|title= Public Patent License, ISO 32000-1: 2008 – PDF 1.7|publisher =Adobe Systems Inc.|year=2008|access-date=January 12, 2023|url-status=live|archive-url=https://web.archive.org/web/20090618144613/http://www.adobe.com/pdf/pdfs/ISO32000-1PublicPatentLicense.pdf|archive-date=June 18, 2009}}</ref>

PDF 1.7, the sixth edition of the PDF specification that became ISO 32000-1, includes some proprietary technologies defined only by Adobe, such as [[Adobe XML Forms Architecture]] (XFA) and [[JavaScript]] extension for Acrobat, which are referenced by ISO 32000-1 as [[normative]] and indispensable for the full implementation of the ISO 32000-1 specification.<ref>{{cite web|date= June 25, 2013|title= Guide for the procurement of standards-based ICT – Elements of Good Practice, Against lock-in: building open ICT systems by making better use of standards in public procurement|url= https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=SWD:2013:0224:FIN:EN:PDF|access-date= January 12, 2023|publisher= European Commission|quote= Example: ISO/IEC 29500, ISO/IEC 26300 and ISO 32000 for document formats reference information that is not accessible by all parties (references to proprietary technology and brand names, incomplete scope or dead web links).|archive-date= September 19, 2020|archive-url= https://web.archive.org/web/20200919174545/https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=SWD:2013:0224:FIN:EN:PDF|url-status= live}}</ref> These proprietary technologies are not standardized, and their specification is published only on Adobe's website.<ref name= "iso-meeting-n603">{{cite web|title=ISO/TC 171/SC 2/WG 8 N 603 – Meeting Report|date=June 27, 2011|url=http://pdf.editme.com/files/pdfREF-meetings/ISO-TC171-SC2-WG8_N0603_SC2WG8_MtgRept_SLC.pdf | work = Edit me | via = Archive |archive-url= https://web.archive.org/web/20121126013025/http://pdf.editme.com/files/pdfREF-meetings/ISO-TC171-SC2-WG8_N0603_SC2WG8_MtgRept_SLC.pdf |url-status=dead|archive-date= November 26, 2012 |quote=XFA is not to be ISO standard just yet. The Committee urges Adobe Systems to submit the XFA Specification, XML Forms Architecture (XFA), to ISO for standardization The Committee is concerned about the stability of the XFA specification Part 2 will reference XFA 3.1}}</ref><ref>{{cite journal|journal=PLOS ONE |date=2013|volume=8|number=9|title=Embedding and publishing interactive, 3-dimensional, scientific figures in Portable Document Format (PDF) files|doi=10.1371/journal.pone.0069446.s001|quote=the implementation of the U3D standard was not complete and proprietary extensions were used.|doi-access=free}}</ref><ref name="rosenthol-adobe-2012">{{cite web |url = http://cdn.parleys.com/p/5148922a0364bc17fc56c6e5/iSUM2012_00_LRO_presentation.pdf |title= PDF and Standards |author=Leonard Rosenthol | publisher = Adobe Systems |year= 2012 |access-date=October 20, 2013 |url-status=dead | via = Parleys |archive-url = https://web.archive.org/web/20130902000323/http://cdn.parleys.com/p/5148922a0364bc17fc56c6e5/iSUM2012_00_LRO_presentation.pdf |archive-date=September 2, 2013 }}</ref> Many of them are not supported by popular third-party implementations of PDF.

ISO published ISO 32000-2 in 2017, available for purchase, replacing the free specification provided by Adobe.<ref name=nowfree/> In December 2020, the second edition of PDF 2.0, ISO 32000-2:2020, was published, with clarifications, corrections, and critical updates to normative references<ref>{{Cite web |url=https://www.pdfa.org/iso-32000-22020-is-now-available/ |title=ISO 32000-2:2020 is now available |publisher=PDFA |date=December 14, 2020 |access-date=February 3, 2021 |archive-date=December 4, 2022 |archive-url=https://web.archive.org/web/20221204112238/https://www.pdfa.org/iso-32000-22020-is-now-available/ |url-status=live }}</ref> (ISO 32000-2 does not include any proprietary technologies as normative references).<ref name=":0">{{cite web|url=https://www.iso.org/standard/75839.html|title=ISO 32000-2 – Document management — Portable document format — Part 2: PDF 2.0|date=January 5, 2021 |publisher=ISO|access-date=February 3, 2021|archive-date=January 28, 2021|archive-url=https://web.archive.org/web/20210128003836/https://www.iso.org/standard/75839.html|url-status=live}}</ref>
In April 2023 the PDF Association made ISO 32000-2 available for download free of charge.<ref name=nowfree>{{cite press release| title=Announcing no-cost access to the latest PDF standard: ISO 32000-2 (PDF 2.0)| publisher=PDF Association| url=https://pdfa.org/sponsored-standards| date=16 June 2023| orig-date=Updated; originally published 5 April 2023| access-date=October 6, 2023| archive-date=September 23, 2023| archive-url=https://web.archive.org/web/20230923202322/https://pdfa.org/sponsored-standards/| url-status=live}}</ref>

== Technical details ==

A PDF file is often a combination of [[vector graphics]], text, and [[bitmap graphics]]. The basic types of content in a PDF are:

* Typeset text stored as content streams (i.e., not encoded in [[plain text]]);
* Vector graphics for illustrations and designs that consist of shapes and lines;
* Raster graphics for photographs and other types of images; and
* Other multimedia objects.

In later PDF revisions, a PDF document can also support links (inside document or web page), forms, JavaScript (initially available as a plugin for Acrobat 3.0), or any other types of embedded contents that can be handled using plug-ins.

PDF combines three technologies:

* An equivalent subset of the PostScript page description programming language but in declarative form, for generating the layout and graphics.
* A [[font embedding|font-embedding]]/replacement system to allow fonts to travel with the documents.
* A structured storage system to bundle these elements and any associated content into a single file, with [[data compression]] where appropriate.

=== PostScript language ===
[[PostScript]] is a [[page description language]] run in an [[Interpreter (computing)|interpreter]] to generate an image.<ref name="Pfiffner_Page_137" /> It can handle graphics and has standard features of [[programming language]]s such as [[conditional (computer programming)|branching]] and [[loop (computing)|looping]].<ref name="Pfiffner_Page_137" /> PDF is a subset of PostScript, simplified to remove such [[control flow]] features, while graphics commands remain.<ref name="Pfiffner_Page_137" />

PostScript was originally designed for a drastically different [[use case]]: transmission of one-way linear print jobs in which the PostScript interpreter would collect a series of commands until it encountered the <code>showpage</code> command, then execute all the commands to render a page as a raster image to a printing device.<ref name="Pfiffner_Page_139">{{cite book |last1=Pfiffner |first1=Pamela |title=Inside the Publishing Revolution: The Adobe Story |date=2003 |publisher=Peachpit Press |location=Berkeley |isbn=0-321-11564-3 |page=139}}</ref> PostScript was not intended for long-term storage and real-time interactive rendering of [[electronic document]]s to [[computer monitor]]s, so there was no need to support anything other than consecutive rendering of pages.<ref name="Pfiffner_Page_139" /> If there was an error in the final printed output, the user would correct it at the application level and send a new print job in the form of an entirely new PostScript file. Thus, any given page in a PostScript file could be accurately rendered only as the cumulative result of executing all preceding commands to draw all previous pages—any of which could affect subsequent pages—plus the commands to draw that particular page, and there was no easy way to bypass that process to skip around to different pages.<ref name="Pfiffner_Page_139" />

Traditionally, to go from PostScript to PDF, a source PostScript file (that is, an executable program) is used as the basis for generating PostScript-like PDF code (see, e.g., [[Adobe Distiller]]). This is done by applying standard [[compiler]] techniques like [[loop unrolling]], [[inline expansion|inlining]] and removing unused branches, resulting in code that is purely declarative and static.<ref name="Pfiffner_Page_139" /> The end result is then packaged into a [[container format]], together with all necessary [[Dependency (computer science)|dependencies]] for correct rendering (external files, graphics, or fonts to which the document refers), and [[Data compression|compressed]]. Modern applications write to printer drivers which directly generate PDF rather than going through PostScript first. 

As a document format, PDF has several advantages over PostScript:

* PDF contains only static [[Declarative programming|declarative]] PostScript code that can be processed as data, and does not require a full program [[Interpreter (computing)|interpreter]] or [[compiler]].<ref name="Pfiffner_Page_139" /> This avoids the complexity and security risks of an engine with such a higher complexity level.
* Like [[Display PostScript]], PDF has supported [[transparency (graphic)|transparent graphics]] since version 1.4, while standard PostScript does not.
* PDF enforces the rule that the code for any particular page cannot affect any other pages.<ref name="Pfiffner_Page_139" /> That rule is strongly recommended for PostScript code too, but has to be implemented explicitly (see, e.g., the [[Document Structuring Conventions]]), as PostScript is a full programming language that allows for such greater flexibilities and is not limited to the concepts of pages and documents.
* All data required for rendering is included within the file itself, improving portability.<ref>{{cite web |url=https://www.adobe.com/content/dam/acom/en/devnet/actionscript/articles/PLRM.pdf|title=PostScript Language Reference]|archive-url=https://web.archive.org/web/20210724120635/https://www.adobe.com/content/dam/acom/en/devnet/actionscript/articles/PLRM.pdf|archive-date=2021-07-24|url-status=dead}}</ref>

Its disadvantages are:

* A loss of flexibility, and limitation to a single use case.{{citation needed|date=December 2023}}
* A (sometimes much) larger file size.<ref>{{cite web |last1=Anton Ertl |first1=Martin |title=What is the PDF format good for? |url=https://www.complang.tuwien.ac.at/anton/why-not-pdf.html |website=complang.tuwien.ac.at |publisher=Vienna University of Technology |access-date=8 April 2024|archive-url=https://web.archive.org/web/20240404031526/https://www.complang.tuwien.ac.at/anton/why-not-pdf.html|archive-date=4 April 2024|url-status=live}}</ref>

PDF since v1.6 supports embedding of interactive 3D documents: 3D drawings can be embedded using [[U3D]] or [[PRC (file format)|PRC]] and various other data formats.<ref name="3d#1">{{cite web |url=https://www.adobe.com/manufacturing/resources/3dformats/ |title=3D supported formats |publisher=Adobe Systems Inc. |date=July 14, 2009 |access-date=February 21, 2010 
|url-status=dead |archive-url=https://web.archive.org/web/20100212072951/http://www.adobe.com/manufacturing/resources/3dformats/ |archive-date=February 12, 2010 }}</ref><ref>{{Cite web|date=November 11, 2022|url=https://helpx.adobe.com/acrobat/kb/supported-file-formats-acrobat-reader.html#main_2D_and_3D_formats__Acrobat_9_Pro_Extended__Adobe_3D_Reviewer_|title=Supported file formats in Acrobat and Reader|publisher=Adobe Systems Inc.|access-date=January 12, 2023|archive-date=December 21, 2022|archive-url=https://web.archive.org/web/20221221111958/https://helpx.adobe.com/acrobat/kb/supported-file-formats-acrobat-reader.html#main_2D_and_3D_formats__Acrobat_9_Pro_Extended__Adobe_3D_Reviewer_|url-status=live}}</ref><ref>{{Cite web|url=https://www.adobe.com/devnet/acrobat/javascript_acrobt_3d.html|title=JavaScript for Acrobat 3D {{!}} Adobe Acrobat Developer Center|publisher=Adobe Systems Inc.|access-date=January 12, 2023|url-status=dead|archive-url=https://web.archive.org/web/20091112231130/https://www.adobe.com/devnet/acrobat/javascript_acrobt_3d.html|archive-date=November 12, 2009}}</ref>

== File format ==

A PDF file is organized using [[ASCII]] characters, except for certain elements that may have binary content.
The file starts with a header containing a [[File format#Magic number|magic number]] (as a readable string) and the version of the format, for example <code>%PDF-1.7</code>. The format is a subset of a COS ("Carousel" Object Structure) format.<ref>{{cite web |url = http://jimpravetz.com/blog/2012/12/in-defense-of-cos/ |archive-url=https://web.archive.org/web/20140502013429/http://jimpravetz.com/blog/2012/12/in-defense-of-cos/ |archive-date=May 2, 2014 |url-status=usurped |title = In Defense of COS, or Why I Love JSON and Hate XML |first = Jim |last = Pravetz |website = jimpravetz.com }}</ref> A COS tree file consists primarily of ''objects'', of which there are nine types:<ref name=":0" />
* [[Boolean data type|Boolean]] values, representing ''true'' or ''false''
* [[Real number]]s
* [[Integer]]s
* [[String (computer science)|Strings]], enclosed within parentheses (<code>(...)</code>) or represented as hexadecimal within single angle brackets (<code>&lt;...&gt;</code>). Strings may contain 8-bit characters.
* Names, starting with a forward slash (<code>/</code>)
* [[Array data type|Arrays]], ordered collections of objects enclosed within square brackets (<code>[...]</code>)
* [[Dictionary (data structure)|Dictionaries]], collections of objects indexed by names enclosed within double angle brackets (<code>&lt;&lt;...&gt;&gt;</code>)
* [[Stream (computing)|Streams]], usually containing large amounts of optionally compressed binary data, preceded by a dictionary and enclosed between the <code>stream</code> and <code>endstream</code> keywords.
* The [[Pointer (computer programming)|null]] object

Comments using 8-bit characters prefixed with the percent sign (<code>%</code>) may be inserted.

Objects may be either ''direct'' (embedded in another object) or ''indirect''. Indirect objects are numbered with an ''object number'' and a ''generation number'' and defined between the <code>obj</code> and <code>endobj</code> keywords if residing in the document root. Beginning with PDF version 1.5, indirect objects (except other streams) may also be located in special streams known as ''object streams'' (marked <code>/Type /ObjStm</code>). This technique enables non-stream objects to have standard stream filters applied to them, reduces the size of files that have large numbers of small indirect objects and is especially useful for ''Tagged PDF''. Object streams do not support specifying an object's ''generation number'' (other than 0).

An index table, also called the cross-reference table, is located near the end of the file and gives the byte offset of each indirect object from the start of the file.<ref>Adobe Systems, PDF Reference, pp. 39–40.</ref> This design allows for efficient [[random access]] to the objects in the file, and also allows for small changes to be made without rewriting the entire file (''incremental update''). Before PDF version 1.5, the table would always be in a special ASCII format, be marked with the <code>xref</code> keyword, and follow the main body composed of indirect objects. Version 1.5 introduced optional ''cross-reference streams'', which have the form of a standard stream object, possibly with filters applied. Such a stream may be used instead of the ASCII cross-reference table and contains the offsets and other information in binary format. The format is flexible in that it allows for integer width specification (using the <code>/W</code> array), so that for example, a document not exceeding 64&nbsp;[[KiB]] in size may dedicate only 2 bytes for object offsets.

At the end of a PDF file is a footer containing
* The <code>startxref</code> keyword followed by an offset to the start of the cross-reference table (starting with the <code>xref</code> keyword) or the cross-reference stream object, followed by
* The <code>%%EOF</code> [[end-of-file]] marker.

If a cross-reference stream is not being used, the footer is preceded by the <code>trailer</code> keyword followed by a dictionary containing information that would otherwise be contained in the cross-reference stream object's dictionary:
* A reference to the root object of the tree structure, also known as the ''catalog'' (<code>/Root</code>)
* The count of indirect objects in the cross-reference table (<code>/Size</code>)
* Other optional information

Within each page, there are one or multiple content streams that describe the text, vector and images being drawn on the page. The content stream is [[Stack-oriented programming language|stack-based]], similar to PostScript.<ref>{{cite web|url = https://pikepdf.readthedocs.io/en/latest/topics/content_streams.html|title = Working with content streams|subject = PikePdf documentation|access-date = May 8, 2022|archive-date = July 5, 2022|archive-url = https://web.archive.org/web/20220705084446/https://pikepdf.readthedocs.io/en/latest/topics/content_streams.html|url-status = live}}</ref>
[[File:Seitengroesse PDF 7.png|thumb|The maximum size of an Acrobat PDF page, superimposed on a map of Europe.]]
There are two layouts to the PDF files: non-linearized (not "optimized") and linearized ("optimized"). Non-linearized PDF files can be smaller than their linear counterparts, though they are slower to access because portions of the data required to assemble pages of the document are scattered throughout the PDF file. Linearized PDF files (also called "optimized" or "web optimized" PDF files) are constructed in a manner that enables them to be read in a Web browser plugin without waiting for the entire file to download, since all objects required for the first page to display are optimally organized at the start of the file.<ref name="pdf-ref">{{cite web|url=https://www.adobe.com/devnet/pdf/pdf_reference.html|title=Adobe Developer Connection: PDF Reference and Adobe Extensions to the PDF Specification|publisher=Adobe Systems Inc.|access-date=December 13, 2010|url-status=dead|archive-url=https://web.archive.org/web/20061115132507/https://www.adobe.com/devnet/pdf/pdf_reference.html|archive-date=November 15, 2006}}</ref> PDF files may be optimized using [[Adobe Acrobat]] software or [[QPDF]].

Page dimensions are not limited by the format itself. However, Adobe Acrobat imposes a limit of 15 million by 15 million inches, or 225 trillion in<sup>2</sup> (145,161&nbsp;km<sup>2</sup>).<ref name="pdf-ref-1.7" />{{rp|1129}}

== Imaging model ==
The basic design of how graphics are represented in PDF is very similar to that of PostScript, except for the use of transparency, which was added in PDF 1.4.

PDF graphics use a [[device independence|device-independent]] [[Cartesian coordinate system]] to describe the surface of a page. A PDF page description can use a [[matrix (mathematics)|matrix]] to [[scale (ratio)|scale]], [[rotate]], or [[Shear mapping|skew]] graphical elements. A key concept in PDF is that of the ''graphics state'', which is a collection of graphical parameters that may be changed, saved, and restored by a ''page description''. PDF has (as of version 2.0) 25 graphics state properties, of which some of the most important are:
* The ''current transformation matrix'' (CTM), which determines the coordinate system
* The ''[[clipping path]]''
* The ''[[color space]]''
* The ''[[alpha compositing|alpha constant]]'', which is a key component of transparency
*''[[Black point compensation]]'' control (introduced in PDF 2.0)

=== Vector graphics ===

As in PostScript, vector graphics in PDF are constructed with ''paths''. Paths are usually composed of lines and cubic [[Bézier curve]]s, but can also be constructed from the outlines of text. Unlike PostScript, PDF does not allow a single path to mix text outlines with lines and curves. Paths can be stroked, filled, fill then stroked, or used for [[clipping path|clipping]]. Strokes and fills can use any color set in the graphics state, including ''patterns''. PDF supports several types of patterns. The simplest is the ''tiling pattern'' in which a piece of artwork is specified to be drawn repeatedly. This may be a ''colored tiling pattern'', with the colors specified in the pattern object, or an ''uncolored tiling pattern'', which defers color specification to the time the pattern is drawn. Beginning with PDF 1.3 there is also a ''shading pattern'', which draws continuously varying colors. There are seven types of shading patterns of which the simplest are the ''axial shading'' (Type 2) and ''radial shading'' (Type 3). <!-- Pictures desperately needed here! -->

=== Raster images ===

Raster images in PDF (called ''Image XObjects'') are represented by dictionaries with an associated stream. The dictionary describes the properties of the image, and the stream contains the image data. (Less commonly, small raster images may be embedded directly in a page description as an ''inline image''.) Images are typically ''filtered'' for compression purposes. Image filters supported in PDF include the following general-purpose filters:

* ''ASCII85Decode'', a filter used to put the stream into 7-bit ASCII,
* ''ASCIIHexDecode'', similar to ASCII85Decode but less compact,
* ''FlateDecode'', a commonly used filter based on the [[deflate]] algorithm defined in {{IETF RFC|1951}} (deflate is also used in the [[gzip]], [[Portable Network Graphics|PNG]], and [[ZIP (file format)|zip]] file formats among others); introduced in PDF 1.2; it can use one of two groups of predictor functions for more compact zlib/deflate compression: ''Predictor 2'' from the [[TIFF]] 6.0 specification and predictors (filters) from the [[Portable Network Graphics|PNG]] specification ({{IETF RFC|2083}}),
* ''LZWDecode'', a filter based on [[LZW]] Compression; it can use one of two groups of predictor functions for more compact LZW compression: ''Predictor 2'' from the TIFF 6.0 specification and predictors (filters) from the PNG specification,
* ''RunLengthDecode'', a simple compression method for streams with repetitive data using the [[run-length encoding]] algorithm and the image-specific filters,
* ''DCTDecode'', a [[lossy]] filter based on the [[JPEG]] standard,
* ''CCITTFaxDecode'', a lossless [[bi-level image|bi-level]] (black/white) filter based on the Group 3 or [[Group 4 compression|Group 4]] [[CCITT]] (ITU-T) [[fax]] compression standard defined in ITU-T [[T.4]] and T.6,
* ''JBIG2Decode'', a lossy or [[lossless]] bi-level (black/white) filter based on the [[JBIG2]] standard, introduced in PDF 1.4, and
* ''JPXDecode'', a lossy or lossless filter based on the [[JPEG 2000]] standard, introduced in PDF 1.5.

Normally all image content in a PDF is embedded in the file. But PDF allows image data to be stored in external files by the use of ''external streams'' or ''Alternate Images''. Standardized subsets of PDF, including [[PDF/A]] and [[PDF/X]], prohibit these features.

=== Text ===

Text in PDF is represented by ''text elements'' in page content streams. A text element specifies that ''characters'' should be drawn at certain positions. The characters are specified using the ''encoding'' of a selected ''font resource''.

A font object in PDF is a description of a digital [[typeface]]. It may either describe the characteristics of a typeface, or it may include an embedded ''font file''. The latter case is called an ''embedded font'' while the former is called an ''unembedded font''. The font files that may be embedded are based on widely used standard digital font formats: [[PostScript fonts|Type 1]] (and its compressed variant CFF), [[TrueType]], and (beginning with PDF 1.6) [[OpenType]]. Additionally PDF supports the Type 3 variant in which the components of the font are described by PDF graphic operators. <!--- Type 3 bit is awkward and should be cleaned up --->

Fourteen typefaces, known as the ''standard 14 fonts'', have a special significance in PDF documents:

* [[Times Roman|Times]] (v3) (in regular, italic, bold, and bold italic)
* [[Courier (typeface)|Courier]] (in regular, oblique, bold and bold oblique)
* [[Helvetica]] (v3) (in regular, oblique, bold and bold oblique)
* [[Symbol (typeface)|Symbol]]
* [[Zapf Dingbats]]

These fonts are sometimes called the ''base fourteen fonts''.<ref>{{cite web|url=http://desktoppub.about.com/od/glossary/g/base14fonts.htm|title=Desktop Publishing: Base 14 Fonts – Definition|last=Howard|first=Jacci|work=About.com Tech|archive-url=https://web.archive.org/web/20160614134144/http://desktoppub.about.com/od/glossary/g/base14fonts.htm|archive-date=June 14, 2016|url-status=dead}}</ref> These fonts, or suitable substitute fonts with the same metrics, should be available in most PDF readers, but they are not ''guaranteed'' to be available in the reader, and may only display correctly if the system has them installed.<ref name="aquarium">{{Cite web|url=http://www.planetpdf.com/planetpdf/pdfs/pdf2k/03e/merz_fontaquarium.pdf|title=The PDF Font Aquarium|last=Merz|first=Thomas|date=June 2003|url-status=usurped|archive-url=https://web.archive.org/web/20110718231502/http://www.planetpdf.com/planetpdf/pdfs/pdf2k/03e/merz_fontaquarium.pdf|archive-date=July 18, 2011}}</ref> Fonts may be substituted if they are not embedded in a PDF.

Within text strings, characters are shown using ''character codes'' (integers) that map to glyphs in the current font using an ''encoding''. There are several predefined encodings, including ''WinAnsi'', ''MacRoman'', and many encodings for East Asian languages and a font can have its own built-in encoding. (Although the WinAnsi and MacRoman encodings are derived from the historical properties of the [[Microsoft Windows|Windows]] and [[classic Mac OS|Macintosh]] operating systems, fonts using these encodings work equally well on any platform.) PDF can specify a predefined encoding to use, the font's built-in encoding or provide a lookup table of differences to a predefined or built-in encoding (not recommended with TrueType fonts).<ref name="pdf-ref-1.7" /> The encoding mechanisms in PDF were designed for Type 1 fonts, and the rules for applying them to TrueType fonts are complex.

For large fonts or fonts with non-standard glyphs, the special encodings ''Identity-H'' (for horizontal writing) and ''Identity-V'' (for vertical) are used. With such fonts, it is necessary to provide a ''ToUnicode'' table if semantic information about the characters is to be preserved.

A text document which is [[Image scanner|scanned]] to PDF without the text being recognised by [[optical character recognition]] (OCR) is an image, with no fonts or text properties.

=== Transparency ===

The original imaging model of PDF was ''opaque,'' similar to PostScript, where each object drawn on the page completely replaced anything previously marked in the same location. In PDF 1.4 the imaging model was extended to allow transparency. When transparency is used, new objects interact with previously marked objects to produce blending effects. The addition of transparency to PDF was done by means of new extensions that were designed to be ignored in products written to PDF 1.3 and earlier specifications. As a result, files that use a small amount of transparency might be viewed acceptably by older viewers, but files making extensive use of transparency could be viewed incorrectly by an older viewer.

The transparency extensions are based on the key concepts of ''transparency groups'', ''blending modes'', ''shape'', and ''alpha''. The model is closely aligned with the features of [[Adobe Illustrator]] version 9. The [[blend modes]] were based on those used by [[Adobe Photoshop]] at the time. When the PDF 1.4 specification was published, the formulas for calculating blend modes were kept secret by Adobe. They have since been published.<ref>{{Cite web|url=https://www.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/pdf_reference_archives/blend_modes.pdf|title=PDF Blend Modes Addendum|url-status=dead|archive-url=https://web.archive.org/web/20111014100004/https://www.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/pdf_reference_archives/blend_modes.pdf|archive-date=October 14, 2011|access-date=January 12, 2023}}</ref>

The concept of a transparency group in PDF specification is independent of existing notions of "group" or "layer" in applications such as Adobe Illustrator. Those groupings reflect logical relationships among objects that are meaningful when editing those objects, but they are not part of the imaging model.

== Additional features ==

=== Logical structure and accessibility<span class="anchor" id="Tagged PDF"></span> ===
{{See also|PDF/A-1|PDF/UA}}

A '''tagged PDF'''<!--boldface per [[WP:R#PLA]]--> (see clause 14.8 in ISO 32000) includes document structure and semantics information to enable reliable text extraction and [[accessibility]].<ref>{{cite web |title=Tagged PDF Best Practice Guide: Syntax |url=https://pdfa.org/wp-content/uploads/2019/06/TaggedPDFBestPracticeGuideSyntax.pdf |website=pdfa.org |publisher=[[PDF Association]] |date=June 2019 |access-date=2024-06-24}}</ref> Technically speaking, tagged PDF is a stylized use of the format that builds on the logical structure framework introduced in PDF 1.3. Tagged PDF defines a set of standard structure types and attributes that allow page content (text, graphics, and images) to be extracted and reused for other purposes.<ref>{{cite web|first=Duff|last=Johnson|date=April 22, 2004|title=What is Tagged PDF?|url=https://www.talkingpdf.org/what-is-tagged-pdf/|url-status=live|archive-url=https://web.archive.org/web/20040807132851/http://www.planetpdf.com/enterprise/article.asp?ContentID=6067|archive-date=August 7, 2004}}</ref>

Tagged PDF is not required in situations where a PDF file is intended only for print. Since the feature is optional, and since the rules for tagged PDF were relatively vague in ISO 32000-1, support for tagged PDF among consuming devices, including [[assistive technology]] (AT), is uneven as of 2021.<ref>{{Cite web|title=Is PDF accessible?|website=DO-IT - Disabilities, Opportunities, Internetworking, and Technology|publisher=University of Washington|date=October 4, 2022|url=https://www.washington.edu/doit/pdf-accessible?1002=|access-date=January 12, 2023|archive-date=February 10, 2023|archive-url=https://web.archive.org/web/20230210114239/https://www.washington.edu/doit/pdf-accessible?1002=|url-status=live}}</ref> ISO 32000-2, however, includes an improved discussion of tagged PDF which is anticipated to facilitate further adoption.

An ISO-standardized subset of PDF specifically targeted at accessibility, [[PDF/UA]], was first published in 2012.

=== Optional Content Groups (layers) ===

With the introduction of PDF version 1.5 (2003) came the concept of Layers. Layers, more formally known as Optional Content Groups (OCGs), refer to sections of content in a PDF document that can be selectively viewed or hidden by document authors or viewers. This capability is useful in CAD drawings, layered artwork, maps, multi-language documents, etc.

Basically, it consists of an Optional Content Properties Dictionary added to the document root. This dictionary contains an array of Optional Content Groups (OCGs), each describing a set of information and each of which may be individually displayed or suppressed, plus a set of Optional Content Configuration Dictionaries, which give the status (Displayed or Suppressed) of the given OCGs.

=== Encryption and signatures ===

A PDF file may be [[encrypted]], for security, in which case a password is needed to view or edit the contents. PDF 2.0 defines 256-bit AES encryption as the standard for PDF 2.0 files. The PDF Reference also defines ways that third parties can define their own encryption systems for PDF.

PDF files may be digitally signed, to provide secure authentication; complete details on implementing digital signatures in PDF are provided in ISO 32000-2.

PDF files may also contain embedded [[digital rights management|DRM]] restrictions that provide further controls that limit copying, editing, or printing. These restrictions depend on the reader software to obey them, so the security they provide is limited.

The standard security provided by PDF consists of two different methods and two different passwords: a ''user password'', which encrypts the file and prevents opening, and an ''owner password'', which specifies operations that should be restricted even when the document is decrypted, which can include modifying, printing, or copying text and graphics out of the document, or adding or modifying text notes and [[#Forms|AcroForm]] fields. The user password encrypts the file, while the owner password does not, instead relying on client software to respect these restrictions. An owner password can easily be removed by software, including some free online services.<ref>{{cite web |url = http://freemypdf.com/ |title = FreeMyPDF.com – Removes passwords from viewable PDFs |website = freemypdf.com |access-date = June 23, 2009 |archive-date = February 20, 2021 |archive-url = https://web.archive.org/web/20210220014724/https://freemypdf.com/ |url-status = live }}</ref> Thus, the use restrictions that a document author places on a PDF document are not secure, and cannot be assured once the file is distributed; this warning is displayed when applying such restrictions using Adobe Acrobat software to create or edit PDF files.

Even without removing the password, most freeware or open source PDF readers ignore the permission "protections" and allow the user to print or make copy of excerpts of the text as if the document were not limited by password protection.<ref>{{cite web|url=http://www.macworld.com/article/1137343/pdf.html|title=Adobe admits new PDF password protection is weaker|first=Jeremy|last=Kirk|date=December 4, 2008|website=[[Macworld]]|publisher=IDG Communications Inc.|access-date=September 14, 2016|archive-date=January 17, 2017|archive-url=https://web.archive.org/web/20170117225255/http://www.macworld.com/article/1137343/pdf.html|url-status=live}}</ref><ref>{{cite web|url=https://www.cs.cmu.edu/~dst/Adobe/Gallery/PDFsecurity.pdf|title= How secure is PDF|first=Bryan|last=Guignard|url-status=dead|archive-url=https://web.archive.org/web/20051024235303/https://www.cs.cmu.edu/~dst/Adobe/Gallery/PDFsecurity.pdf|archive-date=October 24, 2005|publisher=Carnegie Mellon University}}</ref><ref>{{Cite conference|last=Merz|first=Thomas|date=November 2001|url=http://www.planetpdf.com/planetpdf/pdfs/pdf2k/01W/merz_securitykeynote.pdf|title=PDF Security Overview: Strengths and Weaknesses|conference=PDF 2001 conference|location=Scottsdale/Arizona
|url-status=usurped|archive-url=https://web.archive.org/web/20101011050457/http://www.planetpdf.com/planetpdf/pdfs/pdf2k/01W/merz_securitykeynote.pdf|archive-date=October 11, 2010}}</ref>

Beginning with PDF 1.5, Usage rights (UR) signatures are used to enable additional interactive features that are not available by default in a particular PDF viewer application. The signature is used to validate that the permissions have been granted by a [[bona fide]] granting authority. For example, it can be used to allow a user:<ref name="iso32000" />
* To save the PDF document along with a modified form or annotation data
* Import form data files in FDF, XFDF, and text (CSV/TSV) formats
* Export form data files in FDF and XFDF formats
* Submit form data
* [[wikt:instantiate|Instantiate]] new pages from named page templates
* Apply a [[digital signature]] to existing digital signature form field
* Create, delete, modify, copy, import, and export annotations

For example, Adobe Systems grants permissions to enable additional features in Adobe Reader, using [[public-key cryptography]]. Adobe Reader verifies that the signature uses a [[Public key certificate|certificate]] from an Adobe-authorized certificate authority. Any PDF application can use this same mechanism for its own purposes.<ref name="iso32000" />

Under specific circumstances including non-[[Patch (computing)|patched]] systems of the receiver, the information the receiver of a [[Digital signature|digital signed]] document sees can be manipulated by the sender after the document has been signed by the signer.<ref>{{Cite web|url=https://pdf-insecurity.org/signature-shadow/shadow-attacks.html|title=PDF Insecurity Website|website=pdf-insecurity.org|access-date=January 12, 2023|archive-date=March 26, 2023|archive-url=https://web.archive.org/web/20230326024850/https://pdf-insecurity.org/signature-shadow/shadow-attacks.html|url-status=live}}</ref>

[[PAdES]] (''PDF Advanced Electronic Signatures'') is a set of restrictions and extensions to PDF and ISO 32000-1<ref name="ISO 32000-1">{{cite web|title=ISO 32000-1:2008 Document management -- Portable document format -- Part 1: PDF 1.7|url=http://www.iso.org/iso/catalogue_detail.htm?csnumber=51502|publisher=International Organization for Standardization ISO|access-date=March 22, 2016|archive-date=February 10, 2017|archive-url=https://web.archive.org/web/20170210072051/http://www.iso.org/iso/catalogue_detail.htm?csnumber=51502|url-status=live}}</ref> making it suitable for [[advanced electronic signature]]s. This is published by [[ETSI]] as TS 102 778.<ref name="ETSI TS 102 778-1 V1.1.1">{{cite web|title=ETSI TS 102 778-1 - Electronic Signatures and Infrastructures (ESI); PDF Advanced Electronic Signature Profiles; Part 1: PAdES Overview - a framework document for PAdES|version=1.1.1|date=July 2009|url=http://www.etsi.org/deliver/etsi_ts%5C102700_102799%5C10277801%5C01.01.01_60%5Cts_10277801v010101p.pdf|publisher=European Telecommunications Standards Institute ETSI|access-date=January 12, 2023|archive-date=March 8, 2023|archive-url=https://web.archive.org/web/20230308052536/https://www.etsi.org/deliver/etsi_ts%5C102700_102799%5C10277801%5C01.01.01_60%5Cts_10277801v010101p.pdf|url-status=live}}</ref>

=== File attachments ===

PDF files can have file attachments which processors may access and open or save to a local filesystem.<ref>{{cite web|url=https://helpx.adobe.com/uk/acrobat/using/links-attachments-pdfs.html|title=Links and attachments in PDFs|access-date=April 23, 2021|archive-date=April 23, 2021|archive-url=https://web.archive.org/web/20210423155713/https://helpx.adobe.com/uk/acrobat/using/links-attachments-pdfs.html|url-status=live}}</ref>

=== Metadata ===

PDF files can contain two types of metadata.<ref name="pdf-ref-1.7" /> The first is the Document Information Dictionary, a set of key/value fields such as author, title, subject, creation and update dates. This is optional and is referenced from an <code>Info</code> key in the trailer of the file. A small set of fields is defined and can be extended with additional text values if required. This method is deprecated in PDF 2.0.

In PDF 1.4, support was added for Metadata Streams, using the [[Extensible Metadata Platform]] (XMP) to add XML standards-based extensible metadata as used in other file formats. PDF 2.0 allows metadata to be attached to any object in the document, such as information about embedded illustrations, fonts, and images, as well as the whole document (attaching to the document catalog), using an extensible schema.

PDF documents can also contain display settings, including the page display layout and zoom level in a Viewer Preferences object. Adobe Reader uses these settings to override the user's default settings when opening the document.<ref>{{cite journal |url = http://www.adobepress.com/articles/article.asp?p=412914 |title=Getting Familiar with Adobe Reader &gt; Understanding Preferences|date=September 2, 2005|access-date=January 12, 2023 |journal=Adobe Press|publisher=Pearson|url-status=live|archive-url=https://web.archive.org/web/20121023144614/https://www.adobepress.com/articles/article.asp?p=412914|archive-date=October 23, 2012}}</ref> The free Adobe Reader cannot remove these settings.

=== Accessibility ===

PDF files can be created specifically to be accessible to people with disabilities.<ref>{{cite web |url=https://webaim.org/techniques/acrobat/ |title=PDF Accessibility |publisher=WebAIM |access-date=January 12, 2023 |archive-date=January 12, 2023 |archive-url=https://web.archive.org/web/20230112153237/https://webaim.org/techniques/acrobat/ |url-status=live }}</ref><ref>{{cite web |url=http://www.alistapart.com/articles/pdf_accessibility |title=Facts and Opinions About PDF Accessibility |first=Joe |last=Clark |date=August 22, 2005 |access-date=January 12, 2023 |archive-date=January 24, 2013 |archive-url=https://web.archive.org/web/20130124140051/http://alistapart.com/articles/pdf_accessibility |url-status=live }}</ref><ref>{{cite web |title=Best PDF Downloading Website |url=https://pdfdownloadone.com |url-status=live|website=PDF Download One |publisher=The Ohio State University}}</ref><ref>{{cite web |url=https://www.bbc.co.uk/guidelines/futuremedia/accessibility/accessible_pdf.shtml |title=PDF Accessibility Standards|version=1.2 |access-date=January 12, 2023 |url-status=dead |publisher=BBC|archive-date=May 29, 2010|archive-url=https://web.archive.org/web/20100529035503/http://www.bbc.co.uk/guidelines/futuremedia/accessibility/accessible_pdf.shtml}}</ref><ref>{{cite web |url=http://www.csus.edu/training/handouts/workshops/creating_accessible_pdfs.pdf |title=PDF Accessibility |publisher=California State University |access-date=January 12, 2023 |url-status=dead |archive-url=https://web.archive.org/web/20100527215445/http://www.csus.edu/training/handouts/workshops/creating_accessible_pdfs.pdf |archive-date=May 27, 2010|year=2009 }}</ref> PDF file formats in use {{As of|2014|lc=on}} can include tags, text equivalents, captions, audio descriptions, and more. Some software can automatically produce [[PDF/A|tagged PDFs]], but this feature is not always enabled by default.<ref>{{cite web |url=https://help.libreoffice.org/7.4/en-US/text/shared/01/ref_pdf_export.html |title=LibreOffice Help – Export as PDF |access-date=January 12, 2023 |archive-date=January 12, 2023 |archive-url=https://web.archive.org/web/20230112153247/https://help.libreoffice.org/7.4/en-US/text/shared/01/ref_pdf_export.html |url-status=live }}</ref><ref>{{cite web |last=Z. |first=Andrew |url=http://www.oooninja.com/2008/01/generating-pdfa-for-long-term-archiving.html |title=Exporting PDF/A for long-term archiving |date=January 11, 2008 |access-date=September 22, 2012 |archive-date=February 24, 2021 |archive-url=https://web.archive.org/web/20210224185200/https://www.oooninja.com/2008/01/generating-pdfa-for-long-term-archiving.html |url-status=live }}</ref> Leading [[screen reader]]s, including [[JAWS (screen reader)|JAWS]], [[Window-Eyes]], Hal, and [[Kurzweil Educational Systems|Kurzweil 1000 and 3000]] can read tagged PDFs.<ref>{{cite news |url=http://gadgetwise.blogs.nytimes.com/2009/04/10/tip-of-the-week-adobe-readers-read-aloud-feature/ |title=Tip of the Week: Adobe Reader's 'Read Aloud' Feature |access-date=January 12, 2023 |work=The New York Times |date=April 10, 2009 |first=J.D. |last=Biersdorfer |archive-date=November 22, 2020 |archive-url=https://web.archive.org/web/20201122205912/https://gadgetwise.blogs.nytimes.com/2009/04/10/tip-of-the-week-adobe-readers-read-aloud-feature/ |url-status=live }}</ref><ref>{{cite web |url=https://www.adobe.com/accessibility/pdfs/accessing-pdf-sr.pdf |title=Accessing PDF documents with assistive technology: A screen reader user's guide |publisher=Adobe Systems Inc.|access-date=January 12, 2023|url-status=dead|archive-url=https://web.archive.org/web/20080728093103/https://www.adobe.com/accessibility/pdfs/accessing-pdf-sr.pdf|archive-date=July 28, 2008}}</ref> Moreover, tagged PDFs can be re-flowed and magnified for readers with visual impairments. Adding tags to older PDFs and those that are generated from scanned documents can present some challenges.

One of the significant challenges with PDF accessibility is that PDF documents have three distinct views, which, depending on the document's creation, can be inconsistent with each other. The three views are (i) the physical view, (ii) the tags view, and (iii) the content view. The physical view is displayed and printed (what most people consider a PDF document). The tags view is what screen readers and other assistive technologies use to deliver high-quality navigation and reading experience to users with disabilities. The content view is based on the physical order of objects within the PDF's content stream and may be displayed by software that does not fully support the tags' view, such as the Reflow feature in Adobe's Reader.

[[PDF/UA]], the International Standard for accessible PDF based on ISO 32000-1 was first published as ISO 14289–1 in 2012 and establishes normative language for accessible PDF technology.

=== Multimedia ===

''Rich Media PDF'' is a PDF file including interactive content that can be embedded or linked within the file. It can contain images, audio, video content, or buttons. For example, if the interactive PDF is a digital catalog for an E-commerce business, products can be listed on the PDF pages and can be added with images and links to the website and buttons to order directly from the document.

=== Forms ===

''Interactive Forms'' is a mechanism to add forms to the PDF file format. PDF currently supports two different methods for integrating data and PDF forms. Both formats today coexist in the PDF specification:<ref name="iso32000">{{cite web |url=https://www.adobe.com/devnet/acrobat/pdfs/PDF32000_2008.pdf |title=Document Management – Portable Document Format – Part 1: PDF 1.7, First Edition |author=Adobe Systems Inc.|date=July 1, 2008|access-date=January 12, 2023|url-status=dead|archive-url=https://web.archive.org/web/20081203002256/https://www.adobe.com/devnet/acrobat/pdfs/PDF32000_2008.pdf|archive-date=December 3, 2008}}</ref><ref>{{cite web |url=http://gnupdf.org/Forms_Data_Format |title=Gnu PDF – PDF Knowledge – Forms Data Format |archive-url=https://web.archive.org/web/20130101054615/http://www.gnupdf.org/Forms_Data_Format |archive-date=January 1, 2013 |access-date=January 12, 2023|url-status=dead}}</ref><ref>{{cite web |url=http://livedocs.adobe.com/coldfusion/8/htmldocs/help.html?content=formsPDF_02.html |title=About PDF forms |access-date=February 19, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20110429032948/http://livedocs.adobe.com/coldfusion/8/htmldocs/help.html?content=formsPDF_02.html |archive-date=April 29, 2011 |publisher=Adobe Systems Inc.}}</ref><ref>{{cite web|url=https://community.adobe.com/t5/acrobat-sdk-discussions/convert-xfa-form-to-acroform/td-p/1175365|title=Convert XFA Form to AcroForm?|last=Demling|first=Peter|date=July 1, 2008|access-date=January 12, 2023|archive-date=January 12, 2023|archive-url=https://web.archive.org/web/20230112153241/https://community.adobe.com/t5/acrobat-sdk-discussions/convert-xfa-form-to-acroform/td-p/1175365|url-status=live}}</ref>

* AcroForms (also known as Acrobat forms), introduced in the PDF 1.2 format specification and included in all later PDF specifications.
* [[XML Forms Architecture]] (XFA) forms, introduced in the PDF 1.5 format specification. Adobe XFA Forms are not compatible with AcroForms.<ref>{{cite web |url = http://partners.adobe.com/public/developer/tips/topic_tip2.html |title=Migrating from Adobe Acrobat forms to XML forms |access-date=January 12, 2023 |url-status=dead |archive-url = https://web.archive.org/web/20101006151011/http://partners.adobe.com/public/developer/tips/topic_tip2.html |archive-date=October 6, 2010 }}</ref> XFA was deprecated from PDF with PDF 2.0.

AcroForms were introduced in the PDF 1.2 format. AcroForms permit the uses of objects (''e.g.'' [[text box]]es, [[Radio button]]s, ''etc.'') and some code (''e.g.'' JavaScript). Alongside the standard PDF action types, interactive forms (AcroForms) support submitting, resetting, and importing data. The "submit" action transmits the names and values of selected interactive form fields to a specified uniform resource locator (URL). Interactive form field names and values may be submitted in any of the following formats, (depending on the settings of the action's ExportFormat, SubmitPDF, and XFDF flags):<ref name="iso32000" />

; HTML Form format: HTML 4.01 Specification since PDF 1.5; HTML 2.0 since 1.2
; <span class="anchor" id="Forms_Data_Format_(FDF)"></span>Forms Data Format (FDF): based on PDF, uses the same syntax and has essentially the same file structure, but is much simpler than PDF since the body of an FDF document consists of only one required object. Forms Data Format is defined in the PDF specification (since PDF 1.2). The Forms Data Format can be used when submitting form data to a server, receiving the response, and incorporating it into the interactive form. It can also be used to export form data to stand-alone files that can be imported back into the corresponding PDF interactive form. FDF was originally defined in 1996 as part of ISO 32000-2:2017.{{citation needed|date=December 2020}}
; XML Forms Data Format (XFDF): (external XML Forms Data Format Specification, Version 2.0; supported since PDF 1.5; it replaced the "XML" form submission format defined in PDF 1.4) the XML version of Forms Data Format, but the XFDF implements only a subset of FDF containing forms and annotations. Some entries in the FDF dictionary do not have XFDF equivalents – such as the Status, Encoding, JavaScript, Page's keys, EmbeddedFDFs, Differences, and Target. In addition, XFDF does not allow the spawning, or addition, of new pages based on the given data; as can be done when using an FDF file. The XFDF specification is referenced (but not included) in PDF 1.5 specification (and in later versions). It is described separately in ''XML Forms Data Format Specification''.<ref name="xfdf" /> The PDF 1.4 specification allowed form submissions in XML format, but this was replaced by submissions in XFDF format in the PDF 1.5 specification. XFDF conforms to the XML standard. XFDF can be used in the same way as FDF; e.g., form data is submitted to a server, modifications are made, then sent back and the new form data is imported in an interactive form. It can also be used to export form data to stand-alone files that can be imported back into the corresponding PDF interactive form. As of August 2019, XFDF 3.0 is an ISO/IEC standard under the formal name ''ISO 19444-1:2019 - Document management — XML Forms Data Format — Part 1: Use of ISO 32000-2 (XFDF 3.0)''.<ref>{{cite web |title=ISO 19444-1:2019(en) |url=https://www.iso.org/obp/ui/#iso:std:iso:19444:-1:ed-2:v1:en |publisher=The International Organization for Standardization |access-date=December 3, 2020 |archive-date=June 17, 2016 |archive-url=https://web.archive.org/web/20160617031837/https://www.iso.org/obp/ui/#iso:std:iso:19444:-1:ed-2:v1:en |url-status=live }}</ref> This standard is a normative reference of ISO 32000-2.
; PDF

The entire document can be submitted rather than individual fields and values, as was defined in PDF 1.4.

AcroForms can keep form field values in external stand-alone files containing key-value pairs. The external files may use Forms Data Format (FDF) and XML Forms Data Format (XFDF) files.<ref>{{cite web |url=https://helpx.adobe.com/acrobat/kb/acrobat-forms-form-data-web.html |title=Using Acrobat forms and form data on the web |author=Adobe Systems Incorporated |date=September 20, 2022 |access-date=January 12, 2023 |archive-date=January 12, 2023 |archive-url=https://web.archive.org/web/20230112153235/https://helpx.adobe.com/acrobat/kb/acrobat-forms-form-data-web.html |url-status=live }}</ref><ref name="xfdf">{{cite web|title=XML Forms Data Format Specification, version 2|date=September 2007|url=https://www.immagic.com/eLibrary/ARCHIVES/TECH/ADOBE/A070914X.pdf|archive-url=https://web.archive.org/web/20180730100811/https://www.immagic.com/eLibrary/ARCHIVES/TECH/ADOBE/A070914X.pdf|url-status=dead|access-date=February 19, 2010|archive-date=July 30, 2018}}</ref><ref name="fdf-exchange">{{cite web|url=https://www.adobe.com/devnet/acrobat/pdfs/fdf_data_exchange.pdf |title=FDF Data Exchange Specification |date= February 8, 2007 |access-date=January 12, 2023|url-status=dead|archive-url=https://web.archive.org/web/20081203041943/https://www.adobe.com/devnet/acrobat/pdfs/fdf_data_exchange.pdf|archive-date=December 3, 2008}}</ref> The usage rights (UR) signatures define rights for import form data files in FDF, XFDF, and text ([[comma-separated values|CSV]]/[[delimiter-separated values|TSV]]) formats, and export form data files in FDF and XFDF formats.<ref name="iso32000" />

In PDF 1.5, Adobe Systems introduced a proprietary format for forms; [[Adobe XML Forms Architecture]] (XFA). Adobe XFA Forms are not compatible with ISO 32000's AcroForms feature, and most PDF processors do not handle XFA content. The XFA specification is referenced from ISO 32000-1/PDF 1.7 as an external proprietary specification and was entirely deprecated from PDF with ISO 32000-2 (PDF 2.0).

== Licensing ==

Anyone may create applications that can read and write PDF files without having to pay royalties to Adobe Systems; Adobe holds patents to PDF, but licenses them for royalty-free use in developing software complying with its PDF specification.<ref>{{cite web|url=http://partners.adobe.com/public/developer/support/topic_legal_notices.html|title=Developer Resources|publisher=Adobe Systems Inc.|url-status=dead|archive-url=https://web.archive.org/web/20160227041714/http://partners.adobe.com/public/developer/support/topic_legal_notices.html|archive-date=February 27, 2016}}</ref>

== Security==
{{See also|Adobe Acrobat#Security}}

===Changes to content===
In November 2019, researchers from [[Ruhr University Bochum]] and Hackmanit GmbH published attacks on digitally signed PDFs.<ref>{{cite book |url=https://dl.acm.org/doi/10.1145/3319535.3339812 |series=CCS '19 |date=November 6, 2019 |pages=1–14 |publisher=ACM Digital Library, ACM SIGSAC Conference on Computer and Communications Security |doi=10.1145/3319535.3339812 |isbn=9781450367479 |s2cid=199367545 |url-access=subscription |access-date=April 6, 2021 |archive-date=April 26, 2021 |archive-url=https://web.archive.org/web/20210426223722/https://dl.acm.org/doi/10.1145/3319535.3339812 |url-status=live |chapter=1 Trillion Dollar Refund: How to Spoof PDF Signatures |title=Proceedings of the 2019 ACM SIGSAC Conference on Computer and Communications Security |last1=Mladenov |first1=Vladislav |last2=Mainka |first2=Christian |last3=Meyer Zu Selhausen |first3=Karsten |last4=Grothe |first4=Martin |last5=Schwenk |first5=Jörg }}</ref> They showed how to change the visible content in a signed PDF without invalidating the signature in 21 of 22 desktop PDF viewers and 6 of 8 online validation services by abusing implementation flaws.
At the same conference, they additionally showed how to exfiltrate the plaintext of encrypted content in PDFs.<ref>{{cite book |url=https://dl.acm.org/doi/10.1145/3319535.3354214 |series=CCS '19 |date=November 6, 2019 |pages=15–29 |publisher=ACM Digital Library, ACM SIGSAC Conference on Computer and Communications Security |doi=10.1145/3319535.3354214 |isbn=9781450367479 |s2cid=207959243 |url-access=subscription |access-date=April 6, 2021 |archive-date=April 26, 2021 |archive-url=https://web.archive.org/web/20210426223415/https://dl.acm.org/doi/10.1145/3319535.3354214 |url-status=live |chapter=Practical Decryption exFiltration: Breaking PDF Encryption |title=Proceedings of the 2019 ACM SIGSAC Conference on Computer and Communications Security |last1=Müller |first1=Jens |last2=Ising |first2=Fabian |last3=Mladenov |first3=Vladislav |last4=Mainka |first4=Christian |last5=Schinzel |first5=Sebastian |last6=Schwenk |first6=Jörg }}</ref> In 2021, they showed new so-called ''shadow attacks'' on PDFs that abuse the flexibility of features provided in the specification.<ref>{{cite web |url=https://www.ndss-symposium.org/ndss-paper/shadow-attacks-hiding-and-replacing-content-in-signed-pdfs/ |title=Shadow Attacks: Hiding and Replacing Content in Signed PDFs |publisher=Internet Society, The Network and Distributed System Security Symposium |access-date=April 6, 2021 |archive-date=April 21, 2021 |archive-url=https://web.archive.org/web/20210421094100/https://www.ndss-symposium.org/ndss-paper/shadow-attacks-hiding-and-replacing-content-in-signed-pdfs/ |url-status=live }}</ref> An overview of security issues in PDFs regarding [[denial of service]], [[Data breach|information disclosure]], [[data manipulation]], and [[arbitrary code execution]] attacks was presented by Jens Müller.<ref>{{cite web |url=https://www.ndss-symposium.org/ndss-paper/processing-dangerous-paths-on-security-and-privacy-of-the-portable-document-format/ |title=Processing Dangerous Paths – On Security and Privacy of the Portable Document Format |publisher=Internet Society, The Network and Distributed System Security Symposium |access-date=April 6, 2021 |archive-date=April 21, 2021 |archive-url=https://web.archive.org/web/20210421094018/https://www.ndss-symposium.org/ndss-paper/processing-dangerous-paths-on-security-and-privacy-of-the-portable-document-format/ |url-status=live }}</ref><ref>{{cite web |url=https://www.blackhat.com/us-20/briefings/schedule/#portable-document-flaws--20387 |title=Portable Document Flaws 101 |publisher=Blackhat |access-date=April 6, 2021 |archive-date=April 9, 2021 |archive-url=https://web.archive.org/web/20210409131634/https://www.blackhat.com/us-20/briefings/schedule/#portable-document-flaws--20387 |url-status=live }}</ref>

===Malware vulnerability===
PDF files can be infected with viruses, Trojans, and other malware. They can have hidden JavaScript code that might exploit vulnerabilities in a PDF, hidden objects executed when the file that hides them is opened, and, less commonly, a malicious PDF can launch malware.<ref>{{cite web | title=Can PDFs have viruses? Keep your files safe | publisher=Adobe | url=https://www.adobe.com/acrobat/resources/can-pdfs-contain-viruses.html | access-date=3 October 2023 | archive-date=October 4, 2023 | archive-url=https://web.archive.org/web/20231004120143/https://www.adobe.com/acrobat/resources/can-pdfs-contain-viruses.html | url-status=live }}</ref>

PDF attachments carrying viruses were first discovered in 2001. The virus, named ''OUTLOOK.PDFWorm'' or ''Peachy'', uses [[Microsoft Outlook]] to send itself as an attached Adobe PDF file. It was activated with Adobe Acrobat, but not with Acrobat Reader.<ref>Adobe Forums, [https://forums.adobe.com/thread/302989 Announcement: PDF Attachment Virus "Peachy"] {{Webarchive|url=https://web.archive.org/web/20150904151955/https://forums.adobe.com/thread/302989 |date=September 4, 2015 }}, August 15, 2001.</ref>

From time to time, new vulnerabilities are discovered in various versions of Adobe Reader,<ref>{{cite web|url=https://helpx.adobe.com/security.html#readerwin|title=Security bulletins and advisories|publisher=Adobe Systems Inc.|access-date=January 12, 2023|date=January 10, 2023|archive-date=April 6, 2010|archive-url=https://web.archive.org/web/20100406041941/http://www.adobe.com/support/security/#readerwin|url-status=live}}</ref> prompting the company to issue security fixes. Other PDF readers are also susceptible. One aggravating factor is that a PDF reader can be configured to start automatically if a web page has an embedded PDF file, providing a vector for attack. If a malicious web page contains an infected PDF file that takes advantage of a vulnerability in the PDF reader, the system may be compromised even if the browser is secure. Some of these vulnerabilities are a result of the PDF standard allowing PDF documents to be scripted with JavaScript. Disabling JavaScript execution in the PDF reader can help mitigate such future exploits, although it does not protect against exploits in other parts of the PDF viewing software. Security experts say that JavaScript is not essential for a PDF reader and that the security benefit that comes from disabling JavaScript outweighs any compatibility issues caused.<ref>{{Cite web|url=http://www.grc.com/sn/sn-187.txt|title=Steve Gibson – SecurityNow Podcast|date=March 12, 2009|first1=Steve|last1=Gibson|first2=Leo|last2=Laporte|access-date=January 11, 2011|archive-date=May 8, 2020|archive-url=https://web.archive.org/web/20200508100301/https://www.grc.com/sn/sn-187.txt|url-status=live}}</ref> One way of avoiding PDF file exploits is to have a local or web service convert files to another format before viewing.

On March 30, 2010, security researcher Didier Stevens reported an Adobe Reader and Foxit Reader exploit that runs a malicious executable if the user allows it to launch when asked.<ref>{{cite web|url=http://blogs.pcmag.com/securitywatch/2010/03/malicious_pdfs_execute_code_wi.php|title=Malicious PDFs Execute Code Without a Vulnerability|work=PCMAG|url-status=dead|archive-url=https://web.archive.org/web/20100404034752/http://blogs.pcmag.com/securitywatch/2010/03/malicious_pdfs_execute_code_wi.php|archive-date=April 4, 2010}}</ref>

== Software ==
{{Main list|List of PDF software}}

=== Viewers and editors ===

Many PDF viewers are provided free of charge from a variety of sources. Programs to manipulate and edit PDF files are available, usually for purchase.

There are many software options for creating PDFs, including the PDF printing capabilities built into [[macOS]], [[iOS]],<ref>{{Cite web|url=https://ijunkie.com/how-to-create-pdf-web-page-safari-iphone-ipad-ios-11/|title=How to Create a PDF from Web Page on iPhone and iPad in iOS 11|last=Pathak|first=Khamosh|date=October 7, 2017|website=iJunkie|access-date=January 12, 2023|archive-date=January 12, 2023|archive-url=https://web.archive.org/web/20230112153246/https://ijunkie.com/how-to-create-pdf-web-page-safari-iphone-ipad-ios-11/|url-status=live}}</ref> and most [[Linux]] distributions. Much document processing software including [[LibreOffice]], [[Microsoft Office 2007]] (if updated to [[Office 2007#Service Pack 2|SP2]]) and later,<ref>{{cite web|url=http://support.microsoft.com/kb/953195|title=Description of 2007 Microsoft Office Suite Service Pack 2 (SP2)|publisher=[[Microsoft]]|url-status=dead|archive-url=https://web.archive.org/web/20090429212434/http://support.microsoft.com/kb/953195|archive-date=April 29, 2009|access-date=January 12, 2023}}</ref> [[WordPerfect]] 9, and [[Scribus]] can export documents in PDF format. There are many PDF print drivers for Microsoft Windows, the [[pdfTeX]] typesetting system, the [[DocBook]] PDF tools, applications developed around [[Ghostscript]] and [[Adobe Acrobat]] itself as well as [[Adobe InDesign]], [[Adobe FrameMaker]], Adobe Illustrator, Adobe Photoshop, that allow a "PDF printer" to be set up, which when selected sends output to a PDF file instead of a physical printer. [[Google]]'s online office suite [[Google Docs]] allows uploading and saving to PDF. Some web apps offer free PDF editing and annotation tools.

The [[Free Software Foundation]] was "developing a free, high-quality and fully functional set of libraries and programs that implement the PDF file format and associated technologies to the ISO 32000 standard", as one of its [[High priority free software projects|high priority projects]].<ref>On 2014-04-02, a note dated February 10, 2009 referred to [http://www.fsf.org/campaigns/priority.html Current FSF High Priority Free Software Projects] {{Webarchive|url=https://web.archive.org/web/20070810230457/http://www.fsf.org/campaigns/priority.html |date=August 10, 2007 }} as a source. Content of the latter page, however, changes over time.</ref><ref>{{cite web|url=http://gnupdf.org/Goals_and_Motivations|title=Goals and Motivations|publisher=GNUpdf|date=November 28, 2007|website=gnupdf.org|access-date=April 2, 2014|archive-date=July 4, 2014|archive-url=https://web.archive.org/web/20140704114405/http://www.gnupdf.org/Goals_and_Motivations|url-status=live}}</ref> In 2011, however, the GNU PDF project was removed from the list of "high priority projects" due to the maturation of the [[Poppler (software)|Poppler library]],<ref>{{cite web|title=GNU PDF project leaves FSF High Priority Projects list; mission complete!|url=http://www.fsf.org/blogs/community/gnu-pdf-project-leaves-high-priority-projects-list-mission-complete|date=October 6, 2011|first=Matt|last=Lee|publisher=Free Software Foundation|website=fsf.org|archive-date=December 28, 2014|archive-url=https://web.archive.org/web/20141228050435/http://www.fsf.org/blogs/community/gnu-pdf-project-leaves-high-priority-projects-list-mission-complete|url-status=live}}</ref> which has enjoyed wider use in applications such as [[Evince]] with the [[GNOME]] desktop environment. Poppler is based on [[Xpdf]]<ref>{{cite web|url=http://poppler.freedesktop.org/|title=Poppler Homepage|quote=Poppler is a PDF rendering library based on the xpdf-3.0 code base.|access-date=January 12, 2023|archive-date=January 8, 2015|archive-url=https://web.archive.org/web/20150108235708/http://poppler.freedesktop.org/|url-status=live}}</ref><ref>{{cite web|url=http://cgit.freedesktop.org/poppler/poppler/tree/README-XPDF|title=Xpdf License|quote=Xpdf is licensed under the GNU General Public License (GPL), version 2 or 3.|access-date=January 12, 2023|archive-date=April 14, 2013|archive-url=https://archive.today/20130414194348/http://cgit.freedesktop.org/poppler/poppler/tree/README-XPDF|url-status=live}}</ref> code base. There are also commercial development libraries available as listed in [[List of PDF software]].

The [[Apache PDFBox]] project of the [[Apache Software Foundation]] is an open source Java library, licensed under the [[Apache License]], for working with PDF documents.<ref>{{cite web|url=http://pdfbox.apache.org/|url-status=live|title=The Apache PDFBox project- Apache PDFBox 3.0.0 released|date=August 17, 2023|archive-date=January 7, 2023|archive-url=https://web.archive.org/web/20230107234923/https://pdfbox.apache.org/}} Updated for new releases.</ref>

=== Printing ===

[[Raster image processor]]s (RIPs) are used to convert PDF files into a [[raster graphics|raster format]] suitable for imaging onto paper and other media in printers, digital production presses and [[prepress]] in a process known as [[rasterization]]. RIPs capable of processing PDF directly include the Adobe PDF Print Engine<ref>{{cite web|url=https://www.adobe.com/products/pdfprintengine/overview.html|title=Adobe PDF Print Engine|publisher=Adobe Systems Inc.|access-date=August 20, 2014|archive-date=August 22, 2013|archive-url=https://web.archive.org/web/20130822034446/http://www.adobe.com/products/pdfprintengine/overview.html|url-status=live}}</ref> from Adobe Systems and Jaws<ref>{{cite web|url=http://www.globalgraphics.com/products/jaws_rip/|title=Jaws® 3.0 PDF and PostScript RIP SDK|work=globalgraphics.com|access-date=November 26, 2010|archive-date=March 5, 2016|archive-url=https://web.archive.org/web/20160305090728/http://globalgraphics.com/products/jaws_rip|url-status=dead}}</ref> and the [[Harlequin RIP]] from [[Global Graphics]].

In 1993, the Jaws raster image processor from Global Graphics became the first shipping prepress RIP that interpreted PDF natively without conversion to another format. The company released an upgrade to its Harlequin RIP with the same capability in 1997.<ref>{{cite web |url = http://www.globalgraphics.com/products/harlequin-multi-rip |title=Harlequin MultiRIP|access-date=March 2, 2014|url-status=dead|archive-url=https://web.archive.org/web/20140209215413/http://www.globalgraphics.com/products/harlequin-multi-rip/|archive-date=February 9, 2014 }}</ref>

[[Agfa-Gevaert]] introduced and shipped Apogee, the first prepress workflow system based on PDF, in 1997.

Many commercial offset printers have accepted the submission of press-ready PDF files as a print source, specifically the PDF/X-1a subset and variations of the same.<ref>{{cite web|archive-url=https://web.archive.org/web/20090205151505/http://www.prepressx.com/|archive-date=February 5, 2009|url=http://www.prepressx.com/|url-status=usurped|title=Press-Ready PDF Files|quote=For anyone interested in having their graphic project commercially printed directly from digital files or PDFs.|access-date=January 12, 2023}}</ref> The submission of press-ready PDF files is a replacement for the problematic need for receiving collected native working files.

In 2006, PDF was widely accepted as the standard print job format at the [[Open Source Development Labs]] Printing Summit. It is supported as a print job format by the [[CUPS|Common Unix Printing System]] and desktop application projects such as GNOME, [[KDE]], [[Firefox]], [[Mozilla Thunderbird|Thunderbird]], LibreOffice and [[OpenOffice.org|OpenOffice]] have switched to emit print jobs in PDF.<ref>{{cite web |title = PDF as Standard Print Job Format |date=October 23, 2009|url = http://www.linuxfoundation.org/collaborate/workgroups/openprinting/pdf_as_standard_print_job_format |website=The Linux Foundation |publisher=[[Linux Foundation]] |access-date=January 12, 2023|url-status=dead|archive-url=https://web.archive.org/web/20091114130224/https://www.linuxfoundation.org/collaborate/workgroups/openprinting/pdf_as_standard_print_job_format|archive-date=November 14, 2009}}</ref>

Some desktop printers also support direct PDF printing, which can interpret PDF data without external help.

=== Native display model ===
{{unreferenced section|date=November 2023}}
PDF was selected as the "native" [[metafile]] format for Mac OS X, replacing the [[PICT]] format of the earlier [[classic Mac OS]]. The imaging model of the [[Quartz (graphics layer)|Quartz]] graphics layer is based on the model common to [[Display PostScript]] and PDF, leading to the nickname ''Display PDF''. The Preview application can display PDF files, as can version 2.0 and later of the [[Safari (web browser)|Safari]] web browser. System-level support for PDF allows Mac OS X applications to create PDF documents automatically, provided they support the OS-standard printing architecture. The files are then exported in PDF 1.3 format according to the file header. When taking a screenshot under Mac OS X versions 10.0 through 10.3, the image was also captured as a PDF; later versions save screen captures as a PNG file, though this behavior can be set back to PDF if desired.

=== Annotation ===
{{Unreferenced section|date=November 2023}}
{{See also|Comparison of note-taking software}}

Adobe Acrobat is one example of proprietary software that allows the user to annotate, highlight, and add notes to already created PDF files. One UNIX application available as [[free software]] (under the [[GNU General Public License]]) is [[PDFedit]]. The freeware [[Foxit Reader]], available for Microsoft Windows, macOS and Linux, allows annotating documents. Tracker Software's [[PDF-XChange Viewer]] allows annotations and markups without restrictions in its [[freeware]] alternative. [[Apple Inc.|Apple]]'s macOS's integrated PDF viewer, Preview, does also enable annotations as does the open-source software [[Skim (software)|Skim]], with the latter supporting interaction with [[LaTeX]], SyncTeX, and PDFSync and integration with [[BibDesk]] reference management software. Freeware [[Qiqqa]] can create an annotation report that summarizes all the annotations and notes one has made across their library of PDFs. The Text Verification Tool exports differences in documents as annotations and markups.

There are also [[web annotation]] systems that support annotation in pdf and other document formats. In cases where PDFs are expected to have all of the functionality of paper documents, ink annotation is required.

=== Conversion and Information Extraction ===
PDF's emphasis on preserving the visual appearance of documents across different software and hardware platforms poses challenges to the conversion of PDF documents to other [[file format]]s and the targeted [[Information extraction|extraction of information]], such as text, images, tables, [[Bibliography|bibliographic information]], and document [[metadata]]. Numerous tools and source code libraries support these tasks. Several labeled [[dataset]]s to test PDF conversion and information extraction tools exist and have been used for benchmark evaluations of the tool's performance.<ref>{{Citation |last=Meuschke |first=Norman |title=A Benchmark of PDF Information Extraction Tools Using a Multi-task and Multi-domain Evaluation Framework for Academic Documents |date=2023 |work=Information for a Better World: Normality, Virtuality, Physicality, Inclusivity |volume=13972 |pages=383–405 |editor-last=Sserwanga |editor-first=Isaac |url=https://link.springer.com/10.1007/978-3-031-28032-0_31 |place=Cham |publisher=Springer Nature Switzerland |language=en |doi=10.1007/978-3-031-28032-0_31 |isbn=978-3-031-28031-3 |last2=Jagdale |first2=Apurva |last3=Spinde |first3=Timo |last4=Mitrović |first4=Jelena |last5=Gipp |first5=Bela |editor2-last=Goulding |editor2-first=Anne |editor3-last=Moulaison-Sandy |editor3-first=Heather |editor4-last=Du |editor4-first=Jia Tina|arxiv=2303.09957 }}</ref>

== Alternatives ==
{{main|Open XML Paper Specification#Comparison with PDF}}
{{see also|EPUB}}

The [[Open XML Paper Specification]] is a competing format used both as a page description language and as the native print spooler format for Microsoft Windows since [[Windows Vista]].

[[MODCA|Mixed Object: Document Content Architecture]] is a competing format. MO:DCA-P is a part of [[Advanced Function Presentation]].

== See also ==
* [[Web page]]
* [[XSL Formatting Objects]]
* [[Page margin]]
* [[PDF portfolio]]

== References ==
{{Reflist}}

== Further reading ==

* {{cite book | last1 = Hardy | first1 = M. R. B. | last2 = Brailsford | first2 = D. F. | chapter = Mapping and displaying structural transformations between XML and PDF | title = Proceedings of the 2002 ACM symposium on Document engineering – DocEng '02 | pages = 95–102 | year = 2002 | url = https://www.cs.nott.ac.uk/~psadb1/Publications/Download/2002/Hardy02.pdf | doi = 10.1145/585058.585077 | publisher = Proceedings of the 2002 ACM symposium on Document engineering |isbn = 1-58113-594-7 | s2cid = 9371237 }}{{relevance inline|date=May 2022|reason=Why would random conference paper about some particular plugin for Adobe Acrobat be of interest to the reader?}}
* PDF 2.0 {{cite web |url = https://www.iso.org/standard/75839.html |title=ISO 32000-2:2020(en), Document management — Portable document format — Part 2: PDF 2.0 |website = International Organization for Standardization |language = English |access-date = December 16, 2020 }}
* PDF 2.0 {{cite web |url = https://www.iso.org/standard/63534.html |title=ISO 32000-2:2017(en), Document management — Portable document format — Part 2: PDF 2.0 |website = International Organization for Standardization |date=August 3, 2017 |language = English |access-date = January 31, 2019 }}
* [https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/PDF32000_2008.pdf PDF 1.7 (ISO 32000-1:2008)]
* [https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf PDF 1.7] and {{webarchive|url=https://web.archive.org/web/20220306202833/https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdf_reference_archive/pdf_17_errata.pdf|title=errata to 1.7|date=March 6, 2022}}
* [https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.6.pdf PDF 1.6] ({{ISBN|0-321-30474-8}}) and {{webarchive|url=https://web.archive.org/web/20220306152230/https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdf_reference_archive/PDF16Errata.pdf|title=errata to 1.6|date=March 6, 2022}}
* [https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.5_v6.pdf PDF 1.5] and {{webarchive|url=https://web.archive.org/web/20211222122128/https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdf_reference_archive/errata.txt|title=errata to 1.5|date=December 22, 2021}}
* [https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.4.pdf PDF 1.4] ({{ISBN|0-201-75839-3}}) and {{webarchive|url=https://web.archive.org/web/20220306152229/https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdf_reference_archive/PDF14errata.txt|title=errata to 1.4|date=March 6, 2022}}
* [https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.3.pdf PDF 1.3] ({{ISBN|0-201-61588-6}}) and {{webarchive|url=https://web.archive.org/web/20220306152234/https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDFerrata.txt|title=errata to 1.3|date=March 6, 2022}}
* [https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.2.pdf PDF 1.2]
* [https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.0.pdf PDF 1.0] ({{ISBN|0-201-62628-4}})

== External links ==
{{Commons category|Portable Document Format}}
<!--NO LINKS to PDF tools or blogs here-->
* [https://pdfa.org/ PDF Association] – The PDF Association is the industry association for software developers producing or processing PDF files.
** [https://pdfa.org/resource/pdf-specification-index/ PDF Specification Index] at the PDF Association
* {{webarchive |url=https://web.archive.org/web/20101007220449/http://partners.adobe.com/public/developer/tips/topic_tip31.html |title=Adobe PDF 101: Summary of PDF}}
* {{webarchive |url=https://web.archive.org/web/20160413212438/https://www.adobe.com/print/features/psvspdf/ |title=Adobe: PostScript vs. PDF}} – Official introductory comparison of PS, EPS vs. PDF.
* {{webarchive |url=https://web.archive.org/web/20110424013530/http://www.aiim.org/Resources/Archive/Magazine/2007-Jul-Aug/33448 |title = PDF Standards....transitioning the PDF specification from a de facto standard to a de jure standard}} – Information about PDF/E and PDF/UA specification for accessible documents file format
* [https://www.iso.org/standard/38920.html PDF/A-1 ISO standard] published by the [[International Organization for Standardization]] (with corrigenda)
* {{webarchive |url=https://web.archive.org/web/20210116133007/https://www.adobe.com/devnet/pdf/pdf_reference.html |title=PDF Reference and Adobe Extensions to the PDF Specification}}
* [http://preserve.mactech.com/articles/mactech/Vol.15/15.09/PDFIntro/index.html Portable Document Format: An Introduction for Programmers] – Introduction to PDF vs. PostScript and PDF internals (up to v1.3)
* {{webarchive |url=https://web.archive.org/web/20190422013101/http://www.planetpdf.com/enterprise/article.asp?ContentID=6519 |title=The Camelot Paper}} – the paper in which John Warnock outlined the project that created PDF
* {{webarchive |url=https://web.archive.org/web/20160118105015/http://river-valley.zeeba.tv/everything-you-wanted-to-know-about-pdf-but-were-afraid-to-ask/ |title=Everything you wanted to know about PDF but was afraid to ask}} – [https://www.youtube.com/watch?v=poc9PVmFzpc recording of a talk by Leonard Rosenthol] (45 mins) ([[Adobe Systems]]) at TUG 2007

{{Graphics file formats}}
{{Office document file formats}}
{{ISO standards}}
{{Ebooks}}
{{Authority control}}

[[Category:Computer-related introductions in 1993]]
[[Category:Adobe Inc.]]
[[Category:Digital press]]
[[Category:Electronic documents]]
[[Category:Graphics file formats]]
[[Category:ISO standards]]
[[Category:Office document file formats]]
[[Category:Open formats]]
[[Category:Page description languages]]
[[Category:Vector graphics]]
[[Category:PDF software| ]]