When you need to validate a PDF against PDF/UA-1, two free tools dominate: PAC (the PDF Accessibility Checker from the PDF Association) and veraPDF (the open-source reference validator). Both are free, both check PDF/UA, and both come from the same ecosystem — but they serve different purposes. Here's how they compare.
PAC: the visual accessibility checker
PAC (current version PAC 2024) is a free desktop application for Windows and macOS, developed by the PDF Association. Its standout feature is the Screen Reader Preview — it renders the PDF exactly as a screen reader would announce it, so you can see the reading order, structure, and alt text in context. It also includes a low-vision simulator and runs the full PDF/UA-1 conformance check with a plain-language failure report. PAC is the go-to for interactive, visual remediation work.
veraPDF: the reference validator
veraPDF is the open-source, industry-reference validator maintained by the Open Preservation Foundation together with the PDF Association. It checks PDFs against every machine-testable rule of both PDF/A (archival) and PDF/UA (accessibility), reporting each pass and failure with its exact ISO clause. It's the engine compliance reports cite, and it's available as a desktop app, a library, and — via EasyAccessPDF — online in your browser.
How they differ
- Purpose — PAC is interactive and visual (preview, simulation); veraPDF is the authoritative rule-level validator.
- Standards — PAC covers PDF/UA-1; veraPDF covers both PDF/UA-1 and PDF/A (archival).
- Output — PAC gives a human-friendly report plus the screen reader preview; veraPDF gives a detailed, clause-by-clause machine report (ideal as compliance evidence).
- Form factor — PAC is desktop only; veraPDF runs desktop, as a library for pipelines, and online.
They're complementary, not rivals
Most accessibility teams use both: veraPDF for authoritative, repeatable validation (and to generate the report that goes in the compliance file), and PAC for the visual preview that catches issues a rule-checker can't — like confusing reading order or alt text that's technically present but unhelpful. See our full checker comparison for how they stack up against Adobe, CommonLook, and our online tool.
If you don't want to install either
Both PAC and the official veraPDF are desktop downloads. If you need a quick check from a browser, Chromebook, or locked-down work laptop, our free online checker runs the same veraPDF engine with no install — three checks free, report in about 30 seconds. For a deeper walkthrough, see how to check if a PDF is accessible.