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Tag a PDF: How to add tags to an existing PDF

Many PDFs were created without tags – from old templates, scans or print workflows. Retroactive tagging adds a technical base structure so screen readers have a starting point in the document.

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What are PDF tags?

Tags are an invisible structure layer inside a PDF. They describe the role of each piece of content: heading, paragraph, list, table, figure or link. Together they form the structure tree, which assistive technologies such as screen readers use to read the document in a meaningful order and to navigate it. Without tags, a PDF is just a sequence of characters and drawing commands to a screen reader – in the worst case nothing or gibberish is read aloud.

The PDF/UA standard (ISO 14289) requires a fully tagged PDF. Tags are therefore the foundation of every accessible PDF. Our guide Check PDF/UA online explains how to find out whether a document already has tags.

The best route: export accessibly from the source

Tags are most reliable when they are created where the structure is known: in the source document. Word, InDesign and other authoring tools know heading styles, real lists, tables and alternative text for images, and can carry them into the PDF as tags on export. If you have the source file, a clean export is almost always better than any repair after the fact.

Retroactive tagging is the answer when the source is missing, the export produced no tags, or you are dealing with a large archive of legacy PDFs.

How retroactive tagging works in EasyPDFUA

EasyPDFUA is deliberately conservative: it only applies changes that can be derived unambiguously from the existing PDF, and it writes them to a new copy. The original remains untouched. Specifically, the tagger adds:

  • a structure tree (StructTreeRoot) with a Document element and one paragraph tag (P) per page,
  • Link tags with a description for existing link annotations,
  • the flag marking the document as tagged (MarkInfo with Marked true),
  • XMP metadata with the document title and the PDF/UA identifier (pdfuaid:part 1),
  • the document language (/Lang) and title display instead of the file name (DisplayDocTitle),
  • a tab order that follows the document structure (/Tabs /S),
  • missing Unicode mappings for fonts (ToUnicode), where they can be reconstructed unambiguously.

Changes are appended incrementally to the copy, so the original file content is preserved. Signed, encrypted or technically ambiguous PDFs, as well as documents that already contain a MarkInfo entry, are rejected rather than modified at risk.

What automated tagging cannot do

To be clear: a retroactively generated base tree is not yet a fully accessible PDF. EasyPDFUA does not create heading, list, table or figure tags and does not write alternative text. These decisions require an understanding of the content: Is a bold line a heading? Which cells are table headers? What does a chart show?

This follow-up work is done in specialised tools such as Adobe Acrobat Pro, axesPDF or CommonLook – or, where possible, by re-exporting accessibly from the source file. How the requirements of PDF/UA and WCAG differ is covered in PDF/UA vs. WCAG.

Step by step: tag a PDF

  1. Open the application and select a PDF (up to 5 MB for free, up to 50 MB with Premium).
  2. Check or add the document title and language – both are written into the tagged PDF.
  3. Choose Run tagging. If a safe change is not possible, you get a clear explanation why.
  4. Download the new copy. The download is available for 15 minutes and only once.
  5. Validate the result with PAC or veraPDF and add content tags manually.

Validate the result

Retroactive tagging can be incomplete or fail. Always check each generated file with a validator and manually. The messages you will typically see are explained in Common PAC and veraPDF errors. An EasyPDFUA result is not a certification of full PDF/UA conformance.

Frequently asked questions

Can I add tags to a PDF for free?

Yes. The free EasyPDFUA plan lets you tag PDFs up to 5 MB retroactively without entering payment details.

Is a retroactively tagged PDF automatically accessible?

No. Automated tagging creates a technical base structure. Headings, lists, tables and alternative text must be added manually or produced by an accessible export from the source file.

Will my original PDF be changed?

No. EasyPDFUA always creates a new copy and appends the changes to it incrementally. The original remains unchanged.

Why was my PDF rejected?

Signed, encrypted or technically ambiguous PDFs, as well as documents that already contain a MarkInfo entry, are rejected because a change could invalidate the signature or damage existing structures.

Does tagging work with scanned PDFs?

Scanned PDFs without text recognition contain only images, not text. They need optical character recognition (OCR) first before meaningful tagging is possible.