PAC 2021 - The Free PDF Accessibility Checker

Instantly check for WCAG and PDF/UA  compliance of your PDF files.

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What Is PAC?

PAC stands for PDF Accessibility Checker. It was initially released in 2010 and was the first automated PDF/UA compliance validation tool. Having had three previous versions before PAC 2021, PAC is designed to easily identify all of the machine verifiable success criterion of ISO 14289-1 (PDF/UA) and WCAG (Web Content Accessibility Guidelines).


The number of machine verifiable test criterion within the Matterhorn Protocol


The year PAC 1.0 was first released


Number of languages PAC is already available: Danish, English, French, German, Spanish

Why PAC?

PDF/UA and WCAG Compliance Validation

Choose between the two most globally accepted standards related to document accessibility.

Intuitive User Interface

Easy to use features and views make checking a document to a no-brainer.

Simplified Manual Review

The colorful screen reader preview simplifies the manual reviewing of the files. 

Immediate Results of Technical Accessibility

Drag and drop your file onto the user interface and get result immediately.

Both Summary View and Detailed Reporting

Choose between the summary report for decision-makers and the in-depth report with the possibility for precise issue location.

The History of PAC

The History of PAC is closely connected to the history of PDF/UA and the Matterhorn Protocol. Here are some of the most important milestones:

PAC 2021 Logo

08-2021 PAC 2021 released

The PDF/UA Foundation is the new home of PAC. The 2021 release includes enhanced features like the WCAG check set, and a new color contrast check. 

04-2021 Matterhorn Protocol 1.1

The 1.1 release of the Matterhorn Protocol adds a new failure condition and provides several clarifications. 


12-2017 PAC 3 released

The PAC 3.0 release is available with a German user interface and a printable Summary Report. 

07-2014 ICCHP

Roberto Bianchetti, Markus Riesch and Andreas Uebelbacher present their scientific paper “PDF Accessibility Checker (PAC 2): The First Tool to Test PDF Documents for PDF/UA Compliance“ at the 14th International Conference on Computers Helping People with Special Needs (ICCHP) in Paris (France).

PAC 2 screenshot

07-2014 PAC 2 released

Again a world premiere: The release of PAC 2.0 is the first global tool to test PDF documents for PDF/UA compliance. 

08-2013 Matterhorn Protocol 1.0

The Matterhorn Protocol 1.0 is published by the PDF Association. It’s a list of all the possible ways to fail PDF/UA-1, and simplifies the support of the ISO standard for software developers and service providers.

08-2012 PDF/UA-1

PDF/UA is published as an ISO standard (ISO 14289-1:2012). UA stands for Universal Accessibility. It defines all essential requirements for accessible PDF documents, PDF software, and assistive technology for creating, checking, and using PDF/UA compliant files.

PAC 1.3 screenshot

08-2012 PAC 1.3 released

The release of PAC 1.3 introduces a new detailed report. It simplifies locating the issues directly in the document view. 

Markus Erle

07-2012 ICCHP

Markus Erle and Samuel Hofer present their scientific paper “Validity and Semantics – Two Essential Parts of a Backbone for an Automated PDF/UA Compliance Check for PDF Documents“ at the 13th International Conference on Computers Helping People with Special Needs (ICCHP) in Linz (Austria).

German UPI screenshot

09-2011 PAC is picked up worldwide

PAC is picked up by more organizations and experts around the world. For example, the German UPA (Usability Professionals Association) starts referencing it in their Digital Accessibility Guide.

PAC 1 screenshot

03-2010 PAC 1 Beta released

A world premiere: PAC, the first free PDF accessibility checking tool, becomes available. It contains Syntax Checks and the very useful Screen Reader Preview. 

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PAC 2021 Accessibility Conformance Report