Tagging is optional: “A conforming writer is not required to produce tagged PDF documents; however, if it does, it shall conform to these rules.” A tagged file says so in its catalog: “A Tagged PDF document shall also contain a mark information dictionary (see Table 321) with a value of true for the Marked entry.” Its tags, such as headings, paragraphs, lists and figures, each point to the page content they cover, so a screen reader or a reflow view follows them instead of guessing the order from positions. ActualText stands in for content whose drawn form does not spell its words, such as a ligature or a drop capital: “The ActualText value shall be used as a replacement, not a description, for the content, providing text that is equivalent to what a person would see when viewing the content.”

How do you check whether a PDF is tagged?

  • In Acrobat Pro, the accessibility check includes a Tagged PDF rule. Adobe says the check “verifies whether the document conforms to accessibility standards, such as PDF/UA and WCAG 2.0.”
  • With pdfinfo and qpdf. pdfinfo prints a Tagged line; the catalog of a tagged file holds /MarkInfo << /Marked true >> and a /StructTreeRoot. PDF Textfix’s demo letter has neither:
$ pdfinfo "Demo Letter.pdf" | grep Tagged
Tagged:          no
$ qpdf --show-object=1 "Demo Letter.pdf"
<< /Pages 3 0 R /Type /Catalog >>
  • In PDF Textfix’s editor bar, when an edit removes a span’s ActualText: “The accessibility text (ActualText) for this span was removed.”

What does an edit do to the tags?

The words on the page and the words in the tags are separate objects. When a marked span’s ActualText matched the words drawn, PDF Textfix applies the same edit to it, so a screen reader reads the new line; when it did not match, the ActualText is removed and the editor bar says so. The structure tree, with its alternate and accessibility text, is copied as it was, so it can keep the old words. Help > Saving and Privacy says the saved file “can hold the same words”, among them “the accessibility text a tagged file keeps for its pages”.

In some tagged files, a copy of the old words can also stay in the accessibility text of another page that shares it. What saving does to your PDF has the detail.

For privacy, old words left in the tags are still in the file, where text extraction or a screen reader finds them; see Hidden text in a PDF and Redaction versus editing.

How do you keep an edited tagged PDF accessible?

Run an accessibility check over the edited passage and correct its tag, or export a tagged file again from the source. For a document that must not hold the old words, use a redaction tool. What saving does to your PDF lists everything the saved file keeps.

Questions about tagged PDFs

Can you edit a tagged PDF?

Yes. PDF Textfix copies the structure tree as it was and does not edit it; the new text is written where the old text was drawn.

What is the difference between a tagged and an untagged PDF?

In an untagged file, a screen reader or a reflow view guesses the reading order from positions on the page. A tagged file states it.

What does "Tagged PDF: Failed" mean in Acrobat's accessibility check?

Adobe’s help: “If this rule check fails, the document isn’t tagged to specify the correct reading order.” When the check runs with its tagging option on, “Acrobat automatically adds tags to the PDF.” Tags made that way still need checking against the page.