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Tagged PDF: What It Is and How to Check Yours

A tagged PDF contains a structure tree: a hidden outline of the document that labels each piece of content as a heading, paragraph, list, table, figure or other element, and sets the order it is read in. Screen readers and reflow on small screens depend on it. An untagged PDF is, to assistive technology, a flat stream of text with no headings to jump between. Drop a PDF below to see whether it is tagged and whether the tags are usable.

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Check whether a PDF is tagged

What the tags look like

Tags are standard structure types defined in the PDF specification: H1 to H6 for headings, P for paragraphs, L and LI for lists, Table with TH and TD cells, Figure with an alt text attribute, and so on. Each tag points at the marked content on the page it describes. The document catalog also carries a MarkInfo dictionary with Marked set to true.

PDF/UA-1 (ISO 14289-1), the accessibility standard for PDF, requires all real content to be tagged and everything decorative to be marked as an artifact. WCAG 2.1 success criterion 1.3.1 (Info and Relationships) is the requirement tags satisfy for web content.

How to tell whether a PDF is tagged

The checker above reads the structure tree directly with pdf.js, page by page. It reports three states that a simple "Tagged: yes" field in a document properties dialog hides:

  • Not tagged: no structure tree at all. Common for files printed to PDF, scanned, or produced by older tools.
  • Flagged but empty: MarkInfo says Marked is true, but there is no tree behind it. This happens when a tagging step fails part way, or a later tool strips the tree and leaves the flag.
  • Tagged, with problems: a tree exists, but headings skip levels, figures lack alt text or tables have no header cells.

How to tag a PDF

  1. Go back to the source file if you have it. Apply heading styles, alt text and table header rows there.
  2. Export with tags on: in Word for Windows, Save As PDF, Options, "Document structure tags for accessibility"; in Word for Mac, "Best for electronic distribution and accessibility"; in InDesign, "Create Tagged PDF".
  3. Do not print to PDF. Print-to-PDF drivers produce an untagged file.
  4. With no source file, add tags in a remediation tool such as Acrobat Pro, then review the tag tree by hand. Automatic tagging guesses at headings and reading order.
  5. Run the file through a checker again to confirm the tree is present on every page.

This site checks tags and reports what is wrong with them; it does not add them. If the only failure is missing bookmarks, the TOC generator here can build those from your headings.

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Frequently asked questions

Is a tagged PDF the same as an accessible PDF?

No. Tagging is required for an accessible PDF but does not guarantee one. The tags also need a sensible reading order, correct heading levels, meaningful alt text and header cells in tables.

Why does my PDF say it is tagged when a checker says it is not?

The usual cause is a MarkInfo Marked flag with no structure tree behind it. Some viewers report the flag. This checker reads the tree on each page, so it reports when the two disagree.

Does tagging change how the PDF looks?

No. Tags are structural data. The printed and on-screen appearance stays the same.