Before you read another word, try this: open one of your PDFs, press Ctrl+A (Cmd+A on a Mac) to select all the text, and look at what gets highlighted. If nothing highlights, or the selection jumps around in a strange order, you already know something no free PDF accessibility checker will clearly tell you, a screen reader is going to struggle with that document.

That little test takes ten seconds. And it points at the big problem with free checkers: they can only catch what a machine can see. Whether the document actually works for a real person using assistive technology is a different question, and it is the question that matters for Section 508, ADA, and Section 504 compliance.

This article walks through what the popular free tools do well, where they fall short, and how to check a PDF properly. If you would rather have a professional do it, our PDF remediation workspace shows exactly how we take a document from failing to fully compliant.

What an automated PDF accessibility checker actually does

The tools most people reach for are the Adobe Acrobat accessibility checker (built into Acrobat Pro), PAC, the free PDF Accessibility Checker from the PDF/UA Foundation, and various “upload your file” websites. They all work the same basic way: they scan the document’s hidden structure, called tags, and compare it against a rule list.

Think of tags as the machine-readable version of your document layered underneath the visual page. A screen reader never “sees” the page the way you do, it reads the tags. So a checker is really asking one question: do the tags exist, and do they follow the rules?

That is genuinely useful. It is also nowhere near the whole story.

What free checkers catch and what they miss

A checker is good at spotting things that are missing. No tags at all? Flagged. An image with no alt text? Flagged. No document title, no language setting, a form field with no label? Flagged, flagged, flagged. These are real problems and catching them is worthwhile.

What a checker cannot judge is whether anything is right. Here is what that looks like in practice:

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  • • Alt text that says nothing. An image described as “image_final_v2.png” passes every automated test. A blind reader learns nothing from it.
  • • Reading order that jumps around. The tags might read the sidebar first, then the footer, then the headline. Every element is tagged, so the scan comes back clean, but read aloud, the document is word salad.
  • • Headings that lie. If a designer made section titles by just bolding the text, there are no heading tags to navigate by. Or the headings exist but skip from level 1 to level 4. A checker rarely cares. A screen reader user, who navigates by headings the way you skim a page, cares a lot.
  • • Tables tagged in the wrong shape. The tool confirms a table has tags. It cannot tell that the header cells are not connected to the data cells, so a screen reader reads out numbers with no idea what column they belong to.
  • • Form fields with confusing labels. “Text field 47” is a label. It passes. It helps no one.

In our own audits, the issues that actually block people, wrong reading order, meaningless alt text, broken table structure, are almost always in the “passed” column of the automated report. We wrote about the same pattern in why automated PDF checkers miss the most important errors, and it has not changed: a clean scan means “nothing obvious,” not “accessible.”

Why “passed” is not the same as “compliant”

This matters because the laws do not grade on effort. Section 508, the ADA, and the newer Title II rule for state and local governments all point to standards that are about whether a person with a disability can actually use the document, not whether a tool printed a green checkmark. A PDF that “passes” Acrobat’s checker can still be the subject of a complaint, and government agencies publish thousands of PDFs exactly like that. If your organization falls under the Title II PDF requirements, the deadline clock is already running on those documents.

How to check a PDF for 508 compliance properly

A real check combines the tool with a human. Here is the short version of what we do on every document:

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    1. 1. Run the automated checker first. Acrobat’s full check or the PAC checker will surface the missing-and-broken basics in minutes. Fix those.
    1. 1. Open the tags panel and read the order. Does the tag tree follow the document the way a person would read it? Sidebars, captions, and footnotes are the usual troublemakers.
    1. 1. Read every alt text out loud. If it does not describe what the image communicates, rewrite it. Decorative images should be marked as artifacts so screen readers skip them.
    1. 1. Walk the tables and forms. Check that header cells are properly associated and that every form field has a label a stranger would understand.
    1. 1. Listen to it with a screen reader. NVDA is free. Ten minutes of listening tells you more than any report.

When to do it yourself and when to get help

If you have one short, simple document and some patience, the steps above are learnable. Acrobat Pro plus an afternoon will get you there.

The math changes when you have long documents, complex tables, scanned pages, or a whole library to fix. Manual remediation is skilled, detail-heavy work, and doing it badly twice costs more than doing it well once. That is exactly what our manual PDF remediation service is for, every document is fixed and then verified by a human, not just a scanner. Our PDF remediation cost guide explains what that typically runs, and our pricing page has the current numbers.

Frequently asked questions

Is the Adobe Acrobat accessibility checker good enough for compliance?

It is a good first step, not a finish line. Acrobat’s checker verifies that structure exists and flags obvious gaps, but it cannot judge reading order quality, alt text meaning, or table logic. Even Adobe’s own documentation says some checks require manual review.

What is the best free PDF accessibility checker?

PAC (PDF Accessibility Checker) is widely considered the most thorough free tool because it tests against the PDF/UA standard and includes a screen reader preview. Pair it with Acrobat’s checker and you have solid automated coverage, just remember that both stop where human judgment starts.

My PDF passed the checker. Am I done?

Not yet. “Passed” means the machine-checkable rules are satisfied. Before you publish, verify the reading order, the alt text, and the tables yourself, or have someone do a manual review. Those are the areas where most real complaints come from.

The bottom line

Use the free checkers, they are quick, and they catch the easy stuff. Just do not let a green checkmark convince you a document is accessible. If you want a real answer about where your PDFs stand, request a free audit and we will check a sample document by hand, or visit our PDF accessibility workspace to see the full remediation process from start to finish.