Sustainability of Digital Formats: Planning for Library of Congress Collections

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PDF/UA-1, PDF Enhancement for Accessibility, Use of ISO 32000-1

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name ISO 14289-1. Document management applications - Electronic document file format enhancement for accessibility - Part 1: Use of ISO 32000-1
Description

A PDF compliant with the ISO 14289-1 (aka PDF/UA-1) specification is a constrained form of Adobe PDF 1.7 (as defined in ISO 32000-1) intended to ensure accessibility and support for assistive technology, such as screen readers. The UA acronym stands for Universal Accessibility; however, this phrase does not occur in ISO 14289-1.

Requirements for PDF/UA compliance are consistent with the Web Content Accessibility Guidelines (WCAG) 2.0, a W3C Recommendation from 11 December 2008. Among the constraints on a PDF for PDF/UA compliance are the following:

  • All "real content" shall be tagged. Artifacts shall be marked as such and shall not be tagged in the structure tree. The real content of a document comprises objects representing the intent of the document’s author. In contrast, artifacts are objects without semantic significance, often generated in the course of pagination or layout.
  • Content shall be marked in the structure tree with semantically appropriate tags in a logical reading order. The standard imposes detailed usage requirements for headings, tables, and lists to support navigation through assistive technology.
  • All structure types in use shall be standard (as defined in ISO 32000-1:2008, 14.8.4) or mapped to standard structure types, using a role map in the structure tree root (as defined in ISO 32000-1:2008, 14.7.3).
  • Graphics objects (images) that are real content shall be given a Figure tag that includes alternative or replacement text; captions accompanying figures should be tagged as Captions.
  • Information shall not be conveyed by contrast, colour, format or layout, unless the content is tagged to reflect all intended meaning.
  • All information conveyed with sound should also be available without sound.
  • Fonts must be embedded.
  • Dynamic XFA forms are not permitted. Static XFA forms may be used.

In a 2017 blog post entitled An overview of PDF inaccessibility, Jon Metz provides a useful explanation of why people find it "difficult to make their [PDF] documents friendly to people with disabilities."

Production phase A final-state format for delivery to end users. A document compliant with PDF/UA, if not encrypted, is suitable for long-term preservation.
Relationship to other formats
    Subtype of PDF_family, Portable Document Format Family
    Subtype of PDF_1_7, PDF, Version 1.7 (ISO 32000-1:2008)
    Affinity to PDF/A-2a, PDF for Long-term Preservation, Use of ISO 32000-1 (PDF 1.7), Level A Conformance. In an October 2010 presentation on PDF/UA, members of the PDF/UA Working Group stated that PDF/UA "implies eligibility for PDF/A Conformance Level 'a'." However, the PDF/UA-1 standard does not prohibit encryption, which PDF/A does.

Local use Explanation of format description terms

LC experience or existing holdings The Library of Congress provides staff with guidance for creating accessible PDF documents using word-processing software installed on their computers. The guidance refers to the W3C WCAG 2.0 accessibility guidelines and to Section 508 standards (the standard of web accessibility required for websites developed by U.S. government agencies). For more on Section 508, see Adoption in Sustainability Factors and Useful References below.
LC preference Since an unencrypted PDF document compliant with PDF/UA may also comply with requirements for PDF/A, files that conform to PDF/UA in addition to PDF/A are considered a preferred format for page-oriented content by the Library of Congress. See PDF/A_family.

The Library of Congress Recommended Formats Statement (RFS) includes PDF/UA as a preferred format for textual works in digital form, electronic serials, and digital musical compositions. The RFS also includes PDF/UA as an acceptable format for other graphic images - digital.


Sustainability factors Explanation of format description terms

Disclosure

Open standard, published by ISO in July 2012. Developed by working group WG9 of ISO/TC 171 SC2, Document Imaging Applications, Application Issues. See PDF/A_family for information about the secretariat for ISO/TC 171 SC2.

    Documentation

ISO 32000-1:2008 ISO 14289-1:2014. Document management applications -- Electronic document file format enhancement for accessibility -- Part 1: Use of ISO 32000-1 (PDF/UA-1). The standard cannot be used without ISO 32000-1:2008. Document management -- Portable document format -- Part 1: PDF 1.7, which it uses as a normative reference. Also required for understanding of the standard is Web Content Accessibility Guidelines (WCAG) 2.0, a W3C Recommendation from 11 December 2008.

Adoption

In May 2012, an Adobe statement stated, "Adobe fully supports PDF/UA and intends to use and promote it in our PDF authoring tools." As of March 2019, Adobe offers a page describing accessibility by product; the compilers of this resource were only able to identify direct support for creation of PDF/UA files and checking for compliance with the standard in Acrobat Pro. For other products, such as InDesign, Adobe provides guidance for creating accessible documents within the product, before exporting a PDF, and suggests using Acrobat Pro for the final compliance steps for exported PDFs.

Some software vendors specialize in tools to generate accessible documents, including files complying with PDF/UA, including: axes4; CommonLook; and Crawford Technologies. Other vendors that support generation of PDF/UA files can be found in Software Supporting PDF/UA.

Compliance with PDF/UA is sometimes found in requirements applying to governments providing information to the public, often in conjunction with compliance with the more generally applicable WCAG guidelines. For example, accessibility standards for government agencies in the Executive Branch of the U.S. Government, as revised in 2018, are specified in Section 508 of the Rehabilitation Act: Application and Scoping Requirements. The Section 508 requirements state that, "Electronic content shall conform to Level A and Level AA Success Criteria and Conformance Requirements in WCAG 2.0," and require that authoring tools acquired for use within agencies that support export of PDF files must also support export of files compliant with PDF/UA. The website that provides support to agencies for achieving compliance with Section 508 includes the page Create Accessible PDFs, which links to an associated PDF Testing and Remediation Guide. This guide emphasizes that, "Before converting a Microsoft Office document into a PDF, it is important to first verify the document is as accessible as possible."

PDF/UA was designed with assistive technology in mind, such as the screen readers, Job Access With Speech (JAWS), SuperNova, and the open-source NVDA Non-Visual Desktop Access. However, in a 2018 blog post entitled PDF accessibility and reading order, Ted Page points out that the PDF/UA constraint with respect to reading order is inadequate for the popular Read&Write Gold software (now simply Read&Write).

    Licensing and patents See PDF_family.
Transparency

Depends upon compliant software tools to read. Building tools requires sophistication. PDF/UA allows encryption but requires a particular bit in the P key to be set, in order to permit access by assistive technology.

Self-documentation

Support for embedding any form of metadata for a document is good. Metadata in a PDF compliant with PDF/UA must be stored as XMP.

External dependencies

All necessary fonts must be embedded.

Technical protection considerations

PDF/UA allows encryption. PDF/UA requires a particular bit in the P key to be set, in order to permit access to encrypted content by assistive technology.


Quality and functionality factors Explanation of format description terms

Text
Normal rendering Good support. Text characters in a PDF/UA must be mapped to UNICODE and the text must be accessible in logical order. The natural languages used in a document must be declared. To satisfy the requirements of PDF/UA, PDFs created from scanned pages require association of the text. Text derived by OCR must be corrected and tagged to represent the document structure.
Integrity of document structure Many of the constraints on ISO 32000-1 imposed in ISO 14289-1 relate to mandatory inclusion and appropriate use of structural tags.
Integrity of layout and display

PDF is designed to represent the layout of page-oriented documents. However, accessibility requirements may result in a PDF/UA document that is not an exact match in layout to a source document to which it corresponds.

Support for mathematics, formulae, etc.

An image representing a formula must be supplemented with text.

Functionality beyond normal rendering

PDF/UA is designed to be usable through assistive technology. A PDF/UA document should include a document outline that matches the reading order and level of navigational targets, such as headings. Bookmarks and annotations can be embedded.


File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension pdf
The standard does not indicate that a different extension should be used to distinguish PDF from PDF/UA.
Internet Media Type See related format.  See PDF_family.
Magic numbers See related format.  See PDF_family.
Indicator for profile, level, version, etc. See note.  The standard specifies that the PDF/UA version and conformance of a file shall be specified using the PDF/UA Identification extension schema defined in the standard. This schema has one mandatory element: pdfuaid:part (integer). A PDF/UA-1 file should have the integer value 1 for pdfuaid:part.
File signature See related format.  See PDF_family.
Pronom PUID See note
Pronom has no entry for PDF/UA as of March 2019.
Wikidata Title ID Q1606111
See https://www.wikidata.org/wiki/Q1606111.

Notes Explanation of format description terms

General

The creation of PDF/UA files imposes requirements on authors to create well-structured documents using tags that indicate the logical structure of a document, not only its style. For example, headings must be tagged as such with explicit indication of the heading level (e.g. H1, H2), rather than implied using font characteristics. Retrospective conversion of existing PDFs or existing word-processing documents to PDF/UA compliance is not straightforward or easy to automate. See PDF and the User Experience Survey from Karlen Communications, in particular the PDF Remediators Survey Results 2017.

In practice, few PDFs created from scanned historical documents will comply with PDF/UA requirements, because text derived by optical character recognition would need to be corrected and tagged according to the document's logical structure.

History

A working group on PDF/UA (link from 2006 via Internet Archive) was formed by AIIM and Adobe in 2004. The acceptance of PDF as ISO 32000 in 2008 and the publication by WC3 of the second version of its Web Content Accessibility Guidelines led the group to rewrite much of the document, with explicit references to those documents. In 2009, PDF/UA was accepted as a standardization work item by ISO. PDF/UA was approved and published as ISO 14289-1 in 2012.

A new edition, described as a minor update, was published in December 2014. According to an announcement of PDF/UA-1:2014, the final text of ISO 14289-1:2014 was converted to conform to PDF/UA and "ISO will use the PDF/UA-conforming ISO standard as a basis for enhancing its own document production processes towards PDF/UA conformance."

A new version of PDF/UA, based on PDF 2.0 is in preparation as of March 2019.


Format specifications Explanation of format description terms


Useful references

URLs


Last Updated: 04/23/2019