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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) specification is a constrained form of Adobe PDF (as defined in ISO 32000-1) intended to ensure accessibility and support for assistive technology used by a person with a disability. 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 not be tagged.
  • 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 or mapped to standard.
  • 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.
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, Portable Document Format
    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 published PDF/UA standard does not prohibit encryption, which PDF/A does.

Local use Explanation of format description terms

LC experience or existing holdings None.
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.

Sustainability factors Explanation of format description terms

Disclosure

Open standard, published by ISO in July 2012. Developed by the working group ISO/TC 171 SC2, Document Imaging Applications, Application Issues, for which AIIM (The Association for Information and Image Management) acts as secretariat.

    Documentation

ISO 14289-1:2012. 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. 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

As of July 2012, PDF/UA is a new standard. Several developers of PDF Readers have committed to providing support, including Adobe, and the open-source NVDA Non-Visual Desktop Access screen reader.

The extent to which current authoring tools support the creation of PDF/UA documents is unclear as of July 2012. Authoring tools such as word-processors will have to be upgraded (through new versions or add-on modules) to guide users to create compliant documents. In May 2012, an Adobe statement stated, "Adobe fully supports PDF/UA and intends to use and promote it in our PDF authoring tools."

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

    Licensing and patents See PDF.
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.

TBD. 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 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.
Magic numbers See related format.  See PDF/A.
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.

Notes Explanation of format description terms

General

The creation of PDF/UA files will impose 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 will not be straightforward or easy to automate.

History

A working group on PDF/UA 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.


Format specifications Explanation of format description terms


Useful references

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Last Updated: Thursday, 12-Sep-2013 16:54:32 EDT