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PDF is not tagged or the structure tree is incomplete

Tags are the hidden structure of a PDF. They state what is a heading, a paragraph, a list, a table or a figure, and in which order the content is read. A PDF without tags, or with a damaged structure tree, cannot be used reliably with a screen reader. The best fix is to export the PDF again from the source file with tagging switched on.

Updated

Messages you may see

  • Acrobat Accessibility Checker: Tagged PDF - Failed (Document is tagged PDF)
  • PDF/UA-1 (ISO 14289-1) rule 6.2-1: The document catalog dictionary shall include a MarkInfo dictionary containing an entry, Marked, whose value shall be true
  • PDF/UA-1 (ISO 14289-1) rule 7.1-4: Files shall have a Suspects value of false(ISO 32000-1:2008, Table 321)
  • PDF/UA-1 (ISO 14289-1) rule 7.1-11: The logical structure of the conforming file shall be described by a structure hierarchy rooted in the StructTreeRoot entry of the document catalog dictionary, as described in ISO 32000-1:2008, 14.7
  • PDF/UA-1 (ISO 14289-1) rule 7.1-12: A structure element dictionary shall contain the P (parent) entry according to ISO 32000-1:2008, 14.7.2, Table 355
  • PDF/UA-2 (ISO 14289-2) rule 8.2.1-1: The logical structure of the conforming file shall be described by a structure hierarchy rooted in the StructTreeRoot entry of the document catalog dictionary, as described in ISO 32000-2:2020, 14.7
  • PDF/UA-2 (ISO 14289-2) rule 8.2.5.2-1: The structure tree root shall contain a single Document structure element as its only child, as specified in ISO 32000-2:2020, Annex L and ISO/TS 32005
  • Matterhorn Protocol 1.1, 08-003: Suspect entry has a value of true.

What the rule requires

A tagged PDF has a structure tree next to the visible page content. Each structure element (tag) has a type such as P, H1, Table or Figure and points to the pieces of page content it covers. PDF/UA-1 (ISO 14289-1) requires this structure, and automated checkers test the basic conditions with these rules:

  • Rule 6.2-1: the document catalog contains /MarkInfo << /Marked true >>. This flag declares that the file follows the Tagged PDF conventions.
  • Rule 7.1-11: the catalog contains /StructTreeRoot, the root of the structure tree.
  • Rule 7.1-12: every structure element has a /P entry that points to its parent. A missing parent usually means that a tool has damaged the tree.
  • Rule 7.1-4: the /Suspects entry in the MarkInfo dictionary is not true. Converters set /Suspects true when they were unsure whether the tags they created are correct.

For PDF/UA-2 (ISO 14289-2) the corresponding rules are 6.2-1, 8.2.1-1 and 8.2.1-2. PDF/UA-2 also requires (rule 8.2.5.2) that the structure tree root has exactly one child: a Document element in the PDF 2.0 namespace.

The Matterhorn Protocol 1.1 has no separate failure condition for a missing MarkInfo dictionary or structure tree; checkers test these preconditions first. Our report lists them under checkpoint 01 (Real content tagged). A Suspects value of true is Matterhorn failure condition 08-003 (checkpoint 08, OCR validation); our report lists it there.

Tags are the precondition for most other checks. While this rule fails, headings, tables, lists and alternative text cannot be checked at all. After you add tags, the number of reported problems often rises at first; that is expected.

Why it matters

Screen readers read a PDF along its structure tree. Without tags they have to rebuild the reading order from the position of text on the page. Multi-column layouts, sidebars, footnotes and text boxes then come out in the wrong order, and headings, list items and table cells are read as plain text without their role.

Keyboard users who jump from heading to heading, or from table to table, have nothing to jump to. Reflow, which rewraps text for people who need very large magnification or read on small screens, depends on the tags as well. When an untagged PDF is converted to Word, HTML or an accessible text format, the structure is lost.

Common causes

  • The PDF was created with a PDF printer driver (“Print to PDF”) instead of an export function. Printing produces page images of text without structure.
  • The export option for tags was off: in Word Document structure tags for accessibility, in InDesign Create Tagged PDF.
  • The document is a scan. Without text recognition (OCR) it contains only images, and OCR on its own does not always add tags.
  • A tool used after export, for example to merge, split, compress or sign the file, dropped the structure tree or left elements without a parent.
  • The PDF comes from a report generator, a web application or an older library that cannot write tags.
  • A converter or OCR engine set /Suspects true because it could not tag the content reliably.

Example

1 0 obj
<< /Type /Catalog
   /Pages 2 0 R
>>
endobj
Failing: catalog without MarkInfo and StructTreeRoot
1 0 obj
<< /Type /Catalog
   /Pages 2 0 R
   /MarkInfo << /Marked true >>
   /StructTreeRoot 5 0 R
   /Lang (en-GB)
>>
endobj
Fixed: tagged catalog

The structure tree behind /StructTreeRoot then describes the document. Shown as an outline, a small tagged document looks like this:

StructTreeRoot
  Document
    H1      "Annual Report 2025"
    P       "This report describes ..."
    L
      LI
        Lbl     "1."
        LBody   "Budget"
    Figure  Alt="Bar chart: applications per year ..."
Tag tree of a tagged document

How to fix it

Microsoft Word

  1. Choose File > Save As or File > Save a Copy and select PDF as the file type. In the Save As dialog, select Options.
  2. Check Document structure tags for accessibility, confirm with OK and save.
  3. On a Mac, choose File > Save As, PDF and Best for electronic distribution and accessibility (uses Microsoft online service).
  4. In Word for the web, use File > Save As > Download as PDF.

Microsoft recommends running Review > Check Accessibility before saving. Do not use a print-to-PDF printer: the result has no tags, whatever the source document contains.

Adobe InDesign

  1. Choose File > Export and select Adobe PDF (Print) or, for documents with forms, buttons or media, Adobe PDF (Interactive).
  2. Enable Create Tagged PDF. In the interactive export dialog, also enable Use Structure for Tab Order.
  3. Export and open the result in Acrobat to review the tags.

Do not create the PDF with File > Print and a PDF printer. The quality of the tags depends on the preparation in InDesign: paragraph styles mapped to PDF tags, the reading order in the Articles panel and alternative text for images. The other error pages describe these steps.

Adobe Acrobat Pro

If the source file is available, export again from it. If it is not, Acrobat Pro can add tags afterwards:

  1. Choose All tools > Prepare for accessibility > Automatically tag PDF.
  2. If Acrobat finds problems, the Add Tags Report opens in the navigation pane. It lists potential problems by page with links to each one.
  3. Review the result in the Accessibility tags panel (hamburger menu on Windows or View menu on macOS > Show/Hide > Side panels > Accessibility tags) and correct headings, lists, tables and reading order.
  4. For pages where autotagging fails, use All tools > Prepare for accessibility > Fix reading order to tag areas by hand.

If an existing tag tree is badly damaged, Adobe describes removing all tags first: select the root tag in the Tags panel and choose Delete Tag from the options menu, then tag again. For a scanned document, first run All tools > Scan & OCR > Recognize text > In this file.

Check your PDF

Upload the fixed file to see which machine-checkable criteria it meets now. The report lists the remaining problems with their pages.

Open the checker

Questions

Does automatic tagging in Acrobat produce an accessible PDF?
It produces tags, which is a starting point. Adobe's own help points to the Add Tags Report and to manual corrections, and headings, tables and reading order in particular usually need work. Re-exporting from a well-structured source file gives better results.
The file is tagged, but the check still fails. Why?
Either /MarkInfo is missing or false even though a structure tree exists, or some structure elements have no parent, or /Suspects is true. All three can occur when a tool edits a tagged file without maintaining its structure. Re-exporting from the source usually fixes all of them.

Sources

  1. ISO 14289-1:2014 Document management applications – Electronic document file format enhancement for accessibility – Part 1: Use of ISO 32000-1 (PDF/UA-1) – International Organization for Standardization (ISO). Checked on 7 November 2026.
  2. ISO 14289-2:2024 Document management applications – Electronic document file format enhancement for accessibility – Part 2: Use of ISO 32000-2 (PDF/UA-2) – International Organization for Standardization (ISO). Checked on 7 November 2026.
  3. The Matterhorn Protocol 1.1 – PDF Association. Checked on 7 November 2026.
  4. Matterhorn Protocol checks (list of checkpoints and failure conditions) – PDF Association (Tagged PDF School). Checked on 7 November 2026.
  5. Create and verify PDF accessibility, Acrobat Pro – Adobe (Acrobat User Guide), 23 July 2025. Checked on 7 November 2026.
  6. Reading Order tool for PDFs (Adobe Acrobat Pro) – Adobe (Acrobat User Guide), 9 May 2025. Checked on 7 November 2026.
  7. Create accessible PDFs – Microsoft Support. Checked on 8 November 2026.
  8. Creating accessible PDFs – Adobe (InDesign User Guide), 24 May 2023. Checked on 7 November 2026.
  9. Interactive PDF export options in InDesign – Adobe (InDesign User Guide), 2 June 2026. Checked on 7 November 2026.