What PDF/UA and WCAG mean for accessible PDFs

The WCAG guidelines contain success criteria against which you can test content for accessibility. WCAG is intended for all web content and is therefore fairly broadly defined. For example, if you want to make your PDF accessible, the WCAG gives you guidelines for contrast. Such a rule is important for all content. Therefore, an accessible PDF must comply with WCAG guidelines. But WCAG does not include rules for how to make specific technologies or file formats accessible. So if you want to know what modifications to make in the code of the PDF, the WCAG gives you limited guidance. That's where PDF/UA comes in.

PDF/UA standard complements WCAG for PDFs

PDF/UA stands for PDF/Universal Accessibility. This ISO standard is specifically designed to make PDFs accessible. It is actually a variant of the PDF 1.7 standard, but focused on accessibility. That means there is overlap between PDF/UA and WCAG, but there are also differences. Some things are only in WCAG and vice versa. That's why PDF/UA and WCAG are complementary. The legislation around digital accessibility assumes WCAG and thus does not mandate the use of PDF/UA. But do you want the most accessible PDF possible? Make sure it meets the requirements for WCAG and PDF/UA. When we make PDFs accessible we do so according to both standards.

To determine whether your PDF file is PDF/UA compliant, the Matterhorn Protocol was developed. This sounds like the title of a Robert Ludlum book, but it is something quite different. The Matterhorn Protocol is a list of criteria a PDF document must meet for the PDF/UA standard. You can have much of it checked automatically, but several points remain that must be checked by humans. For example, a tool does not know if alternative text fits the image, if all text is tagged, or if content displayed as a list is actually not encoded as a list.

Check your pdf for WCAG and PDF/UA

So for an accessible PDF, it is important that it complies with PDF/UA and WCAG. But how do you know if that is the case? Can you check it yourself? A number of PDF/UA and WCAG criteria must be checked manually. This requires knowledge of these guidelines. Fortunately, many criteria can be checked automatically. Handy, because this way you can remove many errors from your PDFs.

A handy tool to test your PDF for accessibility is the Pleio PDFchecker. Through a simple web interface you can test your pdf for a number of important WCAG 2.1 accessibility criteria and for most PDF/UA requirements. Although the tool helps you find accessibility errors, it does not mean that your pdf is accessible if the tool does not find errors. As mentioned earlier, not all criteria can be checked automatically.

One of the most widely used tools to check PDFs is PAC, which stands for “PDF Accessibility Checker. PAC 2024 is the latest version. This comprehensive tool checks for all automatically measurable criteria of WCAG and PDF/UA. A useful tool is the built-in Screenreader Preview. It allows you to see at a glance how the structure of the document is reflected in the code. That makes it easier to spot any problems.

New developments: PDF 2.0 and PDF/UA-2

PDF/UA is based on PDF 1.7, but PDF 2.0 already exists, so PDF/UA-2 has been defined and is now also an ISO standard. With this, there are now accessibility criteria for PDF 2.0 as well. That means the standard is up to date again and includes new tags. Handy, but do you have to do anything with it? Not really, because you currently can't do much with it. A lot of software (such as Microsoft Office, screen readers and Adobe Acrobat) does not yet support PDF 2.0. Moreover, it is not yet required by law. Forum Standaardisatie mandates PDF 1.7 (and PDF/A-1 and PDF/A-2 for archiving) and recommends PDF/UA. In short, it is good to be aware of the new standard, but for now PDF/UA and WCAG are leading for accessible PDFs.