PDF/UA Details

“PDF/UA makes certain that the PDF format isn’t the source of accessibility problems.”

That does not mean that a PDF/UA-compliant document will always be perfectly accessible—issues like poorly-built Word documents or other source material will, of course, carry their accessibility flaws no matter what format they’re converted into. No one should claim that PDF/UA conformance means that a given document will pass the Web Content Accessibility Guidelines (WCAG) 2.0, and organizations shouldn’t treat PDF/UA as a WCAG stand-in. But conformance does indicate that the authoring process for a given piece of content retains its accessibility level when it’s output as a PDF.

The PDF/UA specification defines conformance for three different aspects of PDF: content, readers, and assistive technology. The authoring tools are intentionally omitted: only the content they produce matters here, and that can only be measured at the individual document level.

A conforming file contains features that are valid according to the PDF 1.7 spec, except for features PDF/UA specifically forbids. It has to be marked as a PDF/UA document as described in Section 5, and meet all the requirements in Section 7 below.

A conforming reader must also be a conforming reader according to PDF 1.7. It will support all the tags, attributes and key values specified for accessibility, and respect when optional content is hidden. It will make the logical reading order available. It will allow AT to inspect artifacts, and its interface must itself be accessible, and not interfere with any AT feature.

Requirements for PDF/UA compliance:

  1. All PDF/UA documents must be tagged PDF. Tags must be semantically appropriate (that is, you can’t just mark everything <p> and be done), and in logical reading order. Artifacts (sometimes referred to as “Background” in Acrobat) must not be tagged. If a PDF does anything non-standard with its tags, those tags have to be remapped to standard PDF tags. Standard tags can’t be overridden.
  2. Content can’t flicker, blink or flash, and it can’t be conveyed solely by color, contrast, formatting,  layout or sound. Image-only PDFs may be created, but their content must also be tagged.
  3. The document must have a title, and it must be displayed in the title bar.
  4. Text must be Unicode. The document’s language, and any changes in language, must be declared.
  5. Graphics must be marked up with the Figure tag, and must have alt text, unless it’s presentational, in which case it’s an Artifact. Groups of images that represent one thought are to be tagged as a single Figure. Captions that go with figures must be tagged as such.
  6. Headings must be nested sequentially (e.g., H1-H2-H3 is acceptable, but H1-H3 is not). Headings can go as deep as necessary (e.g., H1041 is valid, if you’ve used the first 1040 levels). Generic “H” headings are acceptable, but can’t be used interchangeably with numbered headings.
  7. Tables should have headers (“TH” tags) with a Scope attribute.
  8. Lists must be marked up appropriately.
  9. Math equations must be in a Formula tag, with alt text.
  10. Page headers and footers must be marked up as Pagination artifacts, so they’re not read out repeatedly.
  11. Footnotes and endnotes must be marked up with the Note tag.
  12. All optional content configuration dictionaries (a PDF feature which allows content to be hidden conditionally) must be named.
  13. Any embedded files must also be accessible.
  14. Article threads (which allow multicolumn layouts across pages) must retain proper reading order.
  15. Digital signature form fields must be laid out accessibly.
  16. Non-interactive forms have to be tagged with PDF “PrintField” attributes so they will appear as read-only form fields to AT.
  17. Static XFA-based forms are allowed. Dynamic XFA forms are not.
  18. Secured documents must allow AT access.
  19. Documents should have outlines that reflect the reading order and nav hierarchy.
  20. Visible annotations must be represented in the right place in the reading order.
  21. Tab order must be defined.
  22. Links must be tagged, and contain an alternate description.
  23. Metadata tags must be properly set for embedded media.
  24. Actions (i.e., scripting) are allowed. Changes in content or focus must be announced to AT, and cannot set time limits on individual keystrokes.

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