PAC PDF Accessibility Checker vs Includoc

PAC, the PDF Accessibility Checker, is a free Windows app that tests PDFs against PDF/UA (ISO 14289-1), the international standard for accessible PDFs, and against WCAG. Its PDF/UA tests follow the machine-checkable failure conditions in the Matterhorn Protocol, published by the PDF Association. That's why accessibility specialists treat a clean PAC report as the reference check for PDF/UA, and why PAC's messages are what so many people search for. PAC checks documents; it doesn't fix them. Most people know it as PAC 2024. Its publisher, axes4, released PAC 2026 in November 2025, which adds AI-assisted checks that point out items for a person to inspect.

What PAC checks

• PDF/UA: the machine-checkable Matterhorn conditions, covering tags (the hidden structure that tells assistive technology what each part is), role mapping, fonts, metadata, annotations, tables, figures, language and more.
• WCAG: the parts of WCAG that software can test in a PDF.
• Quality checks: added in PAC 2024, these are plausibility checks that go beyond the strict standards, to catch problems that would otherwise need manual testing.
• AI-assisted checks: added in PAC 2026, they run on your own computer and flag things such as text that looks like a heading but isn't tagged as one. axes4 presents them as hints for a human reviewer, not as standard failures, and they don't judge the quality of alt text.
• Tools for the human checks: a screen reader preview, which shows roughly how the document's structure will be presented to assistive technology, and a view of the logical structure, the tag tree.

What PAC can't do is judge meaning. The Matterhorn Protocol itself includes failure conditions that need human judgment, such as whether alt text is accurate, whether the reading order is logical and whether color alone carries meaning. PAC supports those checks with its previews, but a person has to make the call.

Common PAC messages

These are the PAC results people search for most, with our guides to fixing each one:

How to use PAC well

1. Download it from axes4's PAC website (opens another website). It's free and runs on Windows.
2. Open your PDF. PAC runs its checks and shows a summary of PDF/UA and WCAG results.
3. Open the detailed results to see each failed check and where it occurs.
4. Use the screen reader preview and structure view for the checks no software can make, such as reading order and the meaning of alt text.
5. Fix in your editing tool and check again.

Work in a sensible order. Fix the failures that stop people reading, such as untagged content, missing alt text and broken tables, before metadata items. The PDF/UA identifier in particular should be the very last thing you add, once everything else passes.

PAC's limits

• Windows only. Mac users need a Windows virtual machine, or axesCheck, axes4's browser-based checker, which means uploading the file.
• It checks, but doesn't fix. You need Acrobat Pro or another remediation tool to act on the results.
• The language is technical. Messages like "Widget annotations in Form tag" assume you know the tag tree, which makes PAC hard going for people who don't remediate PDFs every day.
• PDF/UA isn't the same as WCAG 2.1 AA. The ADA Title II rule points to WCAG 2.1 Level AA. PAC's WCAG checks cover only what software can test, so a clean PAC report is strong evidence about structure, not a full WCAG review.

How Includoc relates to PAC

We think PAC is excellent, and we use it. Here's how the two fit together:

• We test against the same standard. Includoc validates files with veraPDF, the open-source PDF/UA validator, plus our own checks. Where a result has a PAC equivalent, we show PAC's wording next to it, so you can line our results up with PAC's.
• We fix what PAC finds. Includoc repairs tags, role maps, artifacts, annotations, figures and metadata automatically, rebuilds table structure with headers you confirm, and adds the PDF/UA identifier only when every machine check passes.
• We cross-check with PAC, and you should too. Our quality audits test sample output files with PAC and with screen readers. Different validators sometimes disagree on edge cases, so if PAC flags something in a file we fixed, tell us which check it was.
• PAC is the better tool for some jobs. For an independent second opinion, for checking sensitive files without uploading them anywhere, or for its screen reader preview, use PAC.

Side by side

Ready to compare results? Check a PDF free, then open the same file in PAC. For how the standard itself works, read PDF/UA explained, and for Acrobat's checker, see Adobe Acrobat's checker vs Includoc.

Sources

• PAC: PDF Accessibility Checker (opens another website) and version history (opens another website)
• PDF Association: The Matterhorn Protocol (opens another website)
• veraPDF: veraPDF validator (opens another website)
• ISO: ISO 14289-1:2014, PDF/UA-1 (opens another website)