If you've ever been handed a PDF accessibility report and told "this document is 100% compliant," you've probably had the same reaction a lot of accessibility professionals have: compliant according to whom, checked how?
That question matters more than it might seem. In January 2025, the FTC took action against a major AI accessibility vendor for claiming its automated tool could make websites "fully compliant" with accessibility standards within 48 hours — and settled the case for $1,000,000. The core problem wasn't that the tool didn't work at all. It was that the claim outran what any automated tool can actually verify.
This is exactly why an independent validator matters, and why learning to read one properly is worth ten minutes of your time.
What veraPDF actually is
veraPDF is an open-source, industry-reference validator for PDF/A and PDF/UA (the ISO standard for accessible PDFs — ISO 14289). It's maintained by the PDF Association and was originally developed with EU funding specifically so the industry would have a validator that isn't controlled by any single software vendor with a commercial interest in the result.
That independence is the whole point. A tool that grades its own homework has an obvious incentive to be generous. veraPDF has no such incentive — it checks a PDF against a fixed, published rulebook (the Matterhorn Protocol) and reports exactly what it finds, pass or fail, rule by rule.
What veraPDF actually checks — and what it doesn't
The Matterhorn Protocol defines 31 checkpoints covering 136 specific failure conditions. Of these:
- 87 can be fully determined by software alone — things like whether a heading tag exists, whether an image has an alt-text attribute present, whether the document's structure tree is internally consistent.
- 47 usually require human judgment — whether an image's alt text actually describes the image accurately, whether reading order is logically correct for a human following it, whether a table's header associations make semantic sense.
- 2 have no software test at all.
This is the single most important thing to understand when you open a veraPDF report: a passing result means the document cleared every machine-checkable rule. It does not mean a human has confirmed the document actually makes sense to someone using a screen reader.
Independent research backs this up. Accessibility researcher Karl Groves has estimated that only 25–33% of WCAG success criteria can be reliably evaluated by automated tools at all. A UK Government Digital Service audit found that of 142 known real-world accessibility issues in a test set, even the best automated tools caught only 30–40% of them.
None of this is a knock on veraPDF specifically — it's true of any automated PDF or web accessibility checker. It's a structural limit of what software can verify about human-facing content, not a flaw in the tool.
Reading the report itself
A veraPDF report will typically show you:
- Overall result: compliant or non-compliant against the profile you selected (usually PDF/UA-1).
- Rule-by-rule breakdown: each of the 136-odd checks, marked passed or failed, often grouped by the section of the ISO standard it corresponds to (e.g., clause 7.1 covers whether content is properly tagged or marked as an artifact).
- Failed check counts: how many individual instances of a failure occurred, not just which rule categories failed. A single failed rule might represent one missed alt-text attribute, or five hundred instances of untagged body text — the count tells you the real scope.
What to actually do with a failing report:
- Look at which clause is failing, not just the count. A large number of failures concentrated in one clause (commonly clause 7.1, "tagged content") usually points to one systemic gap — like an entire category of content (headings, form fields, or body paragraphs) never being tagged at all — rather than hundreds of unrelated small problems.
- Don't treat a "compliant" result as a finish line. Given that roughly half of real-world WCAG failure types fall outside what any automated tool can check, a genuinely thorough remediation process pairs an independent validator result with an actual screen-reader pass (NVDA, JAWS, or VoiceOver) — reading through the real document, not just its tag structure.
- Be skeptical of any tool — including validators — that reports a self-graded percentage without showing its work. A specific, itemized failure list you can inspect yourself is worth more than a single number you have to take on faith.
The honest bottom line
An independent, open-source validator like veraPDF can't tell you a document is fully accessible. What it can do is tell you, with full transparency and no commercial incentive to shade the result, exactly which specific, machine-checkable requirements your document does and doesn't meet — and hand you the receipts to check that assessment yourself.
That's a meaningfully different, more honest promise than "100% compliant." It's also, given the regulatory and legal landscape around PDF accessibility right now, the only kind of claim worth actually trusting.