Ensuring that PDF documents are accessible is a critical part of building inclusive, compliant, and user-friendly digital content. A key step in this process is PDF accessibility validation — checking whether your files meet PDF/UA and WCAG accessibility standards.
However, in real-world testing, different PDF/UA validators often produce varying results, even when evaluating the same document. This can create confusion or uncertainty for accessibility professionals and document authors, despite all tools sharing the same goal: helping you achieve accessible, standards-compliant PDFs.
Why PDF Accessibility Validator Results Differ
This comparison is not about ranking or criticizing validation tools, but about helping users understand why these differences occur — and how to interpret them effectively.
Each PDF/UA validation tool is built with the same positive intent: to identify and correct potential accessibility issues.
Yet variations arise naturally due to several factors, including:
- Different interpretations of accessibility techniques and success criteria
- The challenge of converting human judgment into automated checks
- Variations in implementation, rule coverage, and validation logic
It’s also essential to recognize that accessibility validation can never be fully automated. Some aspects of accessibility depend on human understanding, document context, and author intent — factors that no automated validator can perfectly assess.
Defining Your Accessibility Quality Policy
To ensure consistent results, organizations and content creators should establish an accessibility quality policy that defines:
- Acceptable compliance thresholds
- Manual review requirements
- Internal verification processes
True accessibility isn’t about passing every automated check — it’s about making sure your PDFs are readable, navigable, and understandable by everyone, including people using assistive technologies. By understanding the standards, testing logic, and design of each validator, users can apply these tools more effectively and with greater confidence.
How to Use the PDF/UA-1 Validator Comparison
In this PDF/UA-1 Accessibility Validator Comparison, we provide side-by-side tables showing how different validators analyze the same PDF files.
You may notice that some tools flag unique issues or interpret specific errors differently — revealing how automated validation can produce inconsistent or unclear results.
These examples aren’t meant to declare which validator is “right” or “wrong.” Instead, they illustrate how each tool interprets ISO 14289-1 (PDF/UA-1) in its own way or applies additional rules and logic beyond the standard.
Our goal is to make these differences transparent and easy to interpret so you can:
- Understand why one tool flags an issue another overlooks
- Interpret validation results with confidence
- Make informed, expert remediation decisions based on insight, not uncertainty
Think of this comparison as a practical guide for anyone striving to create truly accessible PDFs. Use it to identify clear, well-defined accessibility issues, fix them quickly, and focus on what truly matters — ensuring your content is accessible to every reader.
The goal isn’t to pass every validator without errors or warnings, but to produce genuinely accessible files that effectively deliver your intended information to the reader.
Why Combine Multiple PDF Validators
The most reliable accessibility results often come from combining outputs from multiple validators — such as VeraPDF, PAC, Adobe Preflight PDF/UA or CommonLook PDF Validator. This blended approach leads to more consistent, trustworthy, and actionable accessibility outcomes.
Call for Collaboration and Feedback
We created this comparison to give our users and customers a clear overview of the current state of automated PDF/UA validation and to highlight the complexity behind accessibility testing.
We welcome your feedback and collaboration — whether by:
- Suggesting new validators to include
- Sharing additional test files or rule cases
- Requesting deeper explanations for specific validation results
Our mission is to keep this resource accurate, practical, and up-to-date — a trusted reference that helps you interpret validator results, understand differences, and achieve genuine PDF/UA and WCAG compliance with confidence.
Learn How to Check PDF for Accessibility
Ensure PDF accessibility compliance with PDFix Desktop Lite. Check out our webinar on PDF Validation or explore our blog for more tips!
Frequently Asked Questions
What is PDF/UA and why is it important for accessible PDFs?
PDF/UA (Universal Accessibility), defined by ISO 14289-1, is the standard for making PDF documents fully accessible for people using assistive technologies (e.g. screen readers). It ensures that the document’s structure (tags, reading order, semantics) is correctly defined so that users can navigate, read, and interact with content. Without PDF/UA compliance, a PDF might appear visually correct but remain inaccessible in practice.
Why do different PDF validators produce inconsistent results?
Different validators can interpret the PDF/UA or WCAG rules differently, implement distinct logic, or cover different subsets of validation rules. Each tool may apply different heuristics or fallback logic for complex cases. Some rules require human judgment, which can’t be fully automated. Rule coverage, severity thresholds, and error reporting formats differ. As a result, it’s common for one validator to flag an issue another overlooks. The inconsistencies don’t mean one is wrong — they reflect variation in implementation.
Can PDF accessibility quality be fully validated automatically?
No. Automated tools can detect many structural, tagging, and rule-based issues, but they cannot fully assess context, meaning, or design intent (e.g. whether alt text conveys the right meaning, or whether the reading order truly matches human expectations). Thus, best practice is to combine automated validation with manual review and human expert checks.
Which PDF Validator should I use? Can I use more than one?
There is no one-size-fits-all best validator. Popular tools include veraPDF, PAC, Adobe Preflight PDF/UA, or CommonLook PDF Validator — each with its own strengths and trade-offs in rule coverage and reporting depth. Using multiple validators in tandem is often recommended to cross-check results, compare error reports, and complement them with manual review.
How should I interpret the results from a PDF accessibility validation report?
When reading a validation report, consider: Re-test — after remediation, re-run validators and compare reports to ensure improvements. Severity & context — not all flagged issues are equally critical. Focus first on errors (not just warnings). Rule descriptions vs. tool-specific explanations — understand the underlying standard (e.g. ISO 14289, WCAG) rather than relying solely on the tool’s wording. Prioritize fixes — address structural, tagging, and navigation issues first. Then refine alt text, reading order, metadata, etc.
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Desktop Lite
Free PDF Viewer and PDF Accessibility Checker with built-in industry supported VeraPDF Validator.
Desktop Pro
All-in-one tool for automated PDF accessibility, ensuring PDF/UA and WCAG compliance with customizable remediation workflows.
SDK
AI-powered SDK for PDF accessibility, conversion & data extraction seamlessly integrating into any workflow.
Disclaimer: PDFix provides tools and technology to assist in making your documents accessible, but we do not guarantee 100% document accessibility. Achieving full compliance requires human checks and intervention. Please note that PDFix is a technology provider, not a service provider. The responsibility for document compliance rests with the user.
