Editing PDF (section)

== 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 copies 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 |url=http://wac.osu.edu/pdf/ |title=Accessibility and PDF documents |website=Web Accessibility Center |access-date=January 12, 2023 |url-status=dead |archive-url=https://web.archive.org/web/20100427062242/http://wac.osu.edu/pdf/ |archive-date=April 27, 2010 |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=usurped}}</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).