What lies behind PDF/UA-1 and PDF/UA-2, tags and the Matterhorn Protocol – and why a PDF that looks perfect can still be unreadable.
The invisible second document
A PDF consists of two layers: the visible page image and an invisible structure – the tags. Sighted people read the page image. Screen readers read the tags: which text is a heading? In which order do the paragraphs belong? What is in which table cell? If the tags are missing, a blind person hears nothing but an unordered stream of characters – the document can look perfect and still be completely inaccessible.
PDF/UA-1: the established standard
PDF/UA-1 (ISO 14289-1:2014, “Universal Accessibility”) specifies what this structure has to look like in a PDF based on PDF 1.7 (ISO 32000-1): complete tagging in logical reading order, alternative text for images, correct table and list structure, a declared document language, a meaningful title, embedded fonts, labelled form fields and links.
PDF/UA governs the technology within the file format. What a document has to achieve in terms of content is described by WCAG, which applies to documents via chapter 10 of EN 301 549. EN 301 549 does not make PDF/UA mandatory; its new version V4.1.1, however, explicitly names PDF/UA-1 and PDF/UA-2 as the technical standards for accessible PDFs. In testing practice, the technical side of a PDF is therefore measured against PDF/UA. How it all fits together: WCAG 2.2 and EN 301 549 for PDF documents.
PDF/UA-2: the successor for PDF 2.0
PDF/UA-2 (ISO 14289-2:2024) is based on PDF 2.0 (ISO 32000-2). Its requirements come from the PDF Association’s “Well-Tagged PDF” (WTPDF) specification, whose accessibility level was adopted as an ISO standard. The most important differences:
- Structure elements belong to a namespace (PDF 1.7 or PDF 2.0); custom tags from Word or InDesign are mapped to standard types.
- New and changed structure types, such as Title, FENote for footnotes and endnotes, Em and Strong; the generic H tag is no longer permitted, headings need a level (H1, H2 …).
- Bookmarks and links can point directly to a structure element instead of only to a page.
- More precise requirements for attributes and annotations.
A PDF in version 1.x cannot formally meet PDF/UA-2 – for that it has to be a PDF 2.0 file.
The Matterhorn Protocol: how checking works
The PDF Association’s Matterhorn Protocol translates PDF/UA-1 into 31 checkpoints with 136 failure conditions (current version 1.1 from 2021). 87 of them can be checked by machine – this is done by tools such as veraPDF (the open-source validator on which DokAudit is based) or PAC (with its own checking engine). 47 generally need humans: no machine can decide whether an alternative text is correct in content or whether the reading order is logical. The Matterhorn Protocol refers to PDF/UA-1; for PDF/UA-2, the machine-checkable rules are covered by veraPDF’s PDF/UA-2 validation profile, among others.
UA-1 or UA-2 – what does DokAudit do?
- Checking: DokAudit checks documents with veraPDF against PDF/UA-1 and shows the result of the PDF/UA-2 check alongside.
- UA-1 remains the default: BITV 2.0 (Germany’s federal accessibility ordinance for IT) and EN 301 549 are based on WCAG, and PDF/UA-1 is the established benchmark for proof. In addition, not all viewers and assistive technologies fully support the particular features of PDF 2.0 yet.
- UA-2 on request: if the repaired version passes the UA-1 check, DokAudit can additionally produce a PDF/UA-2 version (PDF 2.0) from it. No visible content changes in the process, only identifiers, metadata, namespaces and link destinations. The version is only provided if it passes the veraPDF check for PDF/UA-2 – otherwise DokAudit lists the remaining rules.
The UA identifier – and why honesty matters
A PDF/UA-compliant document carries an identifier in its metadata. Checking tools raise the alarm if the identifier is missing – or if it has been set although the document does not meet the requirements. The latter is a false claim of conformance. That is why DokAudit only sets the identifier when the standards check actually passes.
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As of: 09/2026. This article provides a general overview and is not legal advice. The statutory and standards texts in force are authoritative; in individual cases the law of a German state may differ.