Learn about the different accessibility checkers for accessible PDF documents (PDF/UA), and the most common mistakes of doing so with Acrobat.

Using the PDF accessibility checker included in Adobe Acrobat Pro to check the accessibility of documents is one of the most common errors found.

But what’s wrong with using Acrobat’s accessibility checker? The quick explanation is that the Acrobat accessibility checker does not adhere to any of the WCAG 2.1 and PDF/UA standards (or any other accessibility standard). You may have noticed that the Acrobat verifier specifically does not mention which standard you are using to check and verify the conformity of the documents. It simply offers a complete check without specifying what type of verification you are doing.

An example, of many, in which the accessibility checker of Acrobat Pro falls short is in the numbered list attribute, also known as the ordered list. Acrobat will not ask for verification of this, but it is crucial for this type of list.

Which PDF accessibility checker should be used?


We recommend the PAC 3 verifier or the PAC 2021 version, to all our customers and students. The latest version is available in five languages: Danish, English, French, German, and Spanish. PAC is the acronym for PDF Accessibility Checker. Evaluate the accessibility of PDF files in accordance with the ISO Standard 14289-1 (PDF/UA). It is a free application that tests the 31 confirmation points (PDF) composed of the 136 failure conditions of the Matterhorn Protocol. These are the specifications of the PDF/UA-1 file format, which assigns the WCAG 2.1 requirements to PDF documents.

PAC allows you to generate valid evaluation reports in PDF/UA format. They indicate the global language, number of tags generated, number of pages and final size of the accessible PDF. Before being delivered, all the requirements checked by PAC must be met and also be fault-free.

Screen capture of a successful PAC Test Report made with 3 version
Made with PAC 3 version
Screen capture of a successful PAC Test Report made with 2021 version
Made with PAC 2021 version

The latest version allows you to verify and generate reports that include color contrast, using the WCAG tab.

Adobe Acrobat Pro

In any case, Acrobat verification serves as a starting point for the early stages of correcting PDF documents. It complements PAC and allows you to generate reports in HTML format in the language of the document we were working on.

Manual verification

Keep in mind that there are some things that can only be checked manually. For example, computers cannot interpret the content and, therefore, cannot decide whether the logical reading order is correct or not. Color contrast, verification of the right use of the tags, the language of the contents, how the alternative texts are written, etc., are other examples in which manual verification and human intervention are required.


For this we also recommend testing with the free Callas plugin called pdfGoHTML. This add-on runs within Acrobat Pro and allows you to see the result of structured and tagged content in an HTML, using the default browser.

Screen reader

Another key aspect in the manual and final check of an accessible PDF is to use a screen reader such as: Apple VoiceOver, Google TalkBack, JAWS, Microsoft Narrator, NVDA, etc.


The NVDA [Non Visual Desktop Access] screen reader is free and one of the most used in the world. It has one-key navigation commands, which makes it friendly and easy to use. It is available for Windows but can be run on macOS through the free VirtualBox (Intel processors) or UTM (Apple Silicon processors) virtualizer.


JAWS [Job Access With Speech] is a commercial screen reader for Windows, developed by Freedom Scientific. It can also be run inside a virtualizer.


Apple VoiceOver is the free support technology that is already installed and ready to use on any Apple device, and is part of the iPadOS, iOS and macOS operating system.


We understand that many companies like to use Acrobat accessibility checker for convenience and because many users can use it as their own way of verifying a document. It is important that you make sure that the documents fully meet the requirements of the users of your company or organization.

When remediate documents, we make sure that both Acrobat Pro and PAC accessibility checkers pass. With each accessible PDF (PDF/UA) remediated and delivered, we provide between two and three complete verification reports.

Request a quote for your project

If you want a quote to convert your files into accessible PDF format, complete the quote request form or send us your files along with an explanation of what you need.

Photography: Glenn Carstens Peters