PDF/UA and veraPDF, explained for non-specialists

PDF/UA: the standard for accessible PDF

PDF/UA ("Universal Accessibility") is an international standard, ISO 14289. It does not describe how a document should look. It describes how the inside of a PDF has to be built so that assistive technology, such as a screen reader, can use it: the content is tagged with its role (heading, paragraph, list, table, figure), the reading order is defined, images have alternative text, decoration is marked so it can be skipped, and the file carries a title and a language.

There are two parts:

• PDF/UA-1 (ISO 14289-1) is built on ISO 32000-1, the PDF 1.7 specification. The standard was first published in 2012; the current edition is ISO 14289-1:2014.
• PDF/UA-2 (ISO 14289-2:2024) applies to PDF 2.0 files. It was published in March 2024 as the successor to PDF/UA-1, and it can use the new tags that PDF 2.0 adds.

Both are sold by ISO and national standards bodies. If your files are not PDF 2.0, PDF/UA-1 is the part to check them against.

PDF/UA sits alongside WCAG, the W3C's Web Content Accessibility Guidelines, which the laws on our deadlines page refer to. PDF/UA covers the technical structure of the file; WCAG covers the experience of the reader, such as colour contrast and clear language. A document can follow one and still miss parts of the other. The deadlines page lists which version of WCAG each law names.

The Matterhorn Protocol: the checklist behind the checkers

The standard itself is written as requirements, which are hard to test directly. The PDF Association's PDF/UA Competence Center turned PDF/UA-1 into a list of every way a file can fail it, called the Matterhorn Protocol. It has 136 "failure conditions" grouped into 31 checkpoints.

The useful idea for non-specialists is that each failure condition is marked as one of two kinds:

• Machine-checkable. Software can decide it on its own. Examples given by PDFlib's summary: an image has no alternative text; a link is not inside a Link tag; the metadata has no document title.
• Needs human judgment. Software cannot decide it. Examples: heading text is not tagged as a heading; content that is visually a list is not tagged as a list; decoration is not marked as decoration; OCR text has recognition errors.

Most failure conditions are machine-checkable, but the human ones decide whether the structure actually matches what is on the page.

veraPDF: a free, open-source checker

veraPDF is a file-format validator led by the Open Preservation Foundation and the PDF Association. It is open source, dual-licensed under GPLv3+ and MPLv2+, and runs on Windows, Mac and Linux with Java. It has a desktop interface for single files and a command-line tool for batches. It was designed with digital archivists in mind and validates PDF/A (the archiving standard) as well as PDF/UA parts 1 and 2. The latest release when we checked was 1.30.3, published on 9 October 2026.

Its documentation is explicit about scope: for PDF/UA, veraPDF performs only the machine-verifiable checks, and it refers to the Matterhorn Protocol for which checks are machine and which are human. PAC, a free Windows checker, also implements the Matterhorn Protocol.

What a veraPDF pass means

A pass means the file has no failure in any of the machine-checkable rules of the profile you chose. In practice that tells you:

• the file is marked as tagged and has a structure tree;
• its metadata has a title, and the title is set to display instead of the file name;
• the language of its text can be determined;
• every element tagged as a figure has some alternative text;
• form fields are tagged as form fields and have a label;
• the fonts used are embedded in the file.

veraPDF publishes the full list of PDF/UA-1 rules it tests, each with the wording from the standard.

What a pass does not mean

• It does not mean the headings are the real headings, the reading order is the order a person would read, or the table headers are the right cells.
• It does not mean the alt text describes the picture. "Image" passes the machine test as well as a good description does.
• It does not check colour contrast, plain language or the meaning of the content.
• It is not a stamp of approval. No checker can say a document meets a law; a pass is one piece of evidence, alongside a human review.

So a good routine is: run veraPDF or PAC to clear the machine failures, then have a person look at the structure, ideally by listening to part of the document with a screen reader. For a backlog, the guide to remediating many PDFs shows how to fit both checks into the workflow, and the guide to checking a PDF compares free tools.

Sources

• PDFlib knowledge base: The PDF/UA standard (ISO 14289, 2012; ISO 14289-1:2014)
• Estonian Centre for Standardisation: ISO 14289-2:2024 (PDF/UA-2) (valid from 13 March 2024)
• PDFlib knowledge base: Matterhorn Protocol (136 failure conditions in 31 checkpoints, examples)
• veraPDF: About (led by OPF and the PDF Association; licences; PDF/UA parts 1 and 2 machine checks)
• veraPDF documentation: Validation (PDF/UA: only machine-verifiable checks)
• veraPDF validation profiles: PDF/UA-1 rules
• veraPDF on GitHub: releases (1.30.3, 9 October 2026)
• Virginia Tech TLOS: PAC (PDF Accessibility Checker)