Avery Hymel

Most Important PDF Accessibility Standards

As organizations dive into the often murky waters of PDF accessibility, questions on standards are inevitable. How many standards are there, and why do they exist? How do I know which standard to aim for? What are the differences between them? Where do I begin?

These concerns are normal. Nobody wants to make the wrong choice, waste valuable time, or risk doing something wrong. My goal is to share the details of the different standard types, provide some of the most significant distinctions between them, advise what standards you should be using, and showcase the Allyant recommendation for guaranteeing standards compliance.

Before we delve into the individual standards, let’s look at the two types of electronic document standards.

Electronic Document Standards

Structural standards offer guidelines for creating a PDF and checking some of its more structure-related requirements. For example, if a document has a graphical element, such as a FormXObject, a structural standard will flag it if it is not in a Figure tag.

Accessibility standards address the requirements for a document to function appropriately with assistive technology and provide access to the content. For example, if that FormXObject is in a Figure tag, an accessibility standard will flag it if it is not given Alternative (or Actual) text.

Both structural and accessibility standards serve specialized purposes and are crucial to overall compliance.


ISO-32000-1 (version 1) is a structural standard. While a more recently released structural standard (ISO 32000-2 – version 2) exists, ISO-32000-1 is the one most processors and assistive technologies support.

This is the most commonly used structural standard until the technology catches up and supports the newer standard.

If you use Allyant’s CommonLook PDF to remediate (fix) your PDFs, you will find that ISO-32000-1 is the only available structural standard.

For more context, the latest ISO 32000-2 release was introduced in December 2020. PDF/UA-2 has been published as of early 2024. It is our expectation that in the near future, support for ISO-3200-2 and PDF/UA-2 will be more readily available.

It’s also important to note that Allyant has two people who actively participate in these standards-writing activities. So, we have our finger on the pulse, and when the standards are supported, Allyant will support them as well!

Section 508

Accessibility standards, however, offer more options. Section 508, originally from the American Rehabilitation Act, was enacted to eliminate barriers between audiences and information technology.

While a staple of electronic accessibility for many years, this law was revised in 2017 to reference WCAG 2.0 (or the Web Content Accessibility Guidelines) — a set of guidelines to ensure accessibility. WCAG 2.0 has since been updated to WCAG 2.1, and more recently 2.2.

Within the general Web Content Accessibility Guidelines (both 2.0, 2.1 and 2.2), there are A (single-A), AA (double-A), and AAA (triple-A) Success Criteria that address different levels of compliance within the standard.

As you proceed from A to AAA, the levels grow more involved, meaning that AAA-compliant documents are more accessible than A-compliant documents.

Web Content Accessibility Guidelines (WCAG)

In 1997, the World Wide Web Consortium (W3C)’s Web Accessibility Initiative (WAI) created international standards for the Internet in an effort to improve online experiences for people with disabilities.

Though these Web Content Accessibility Guidelines (WCAG) were originally written specifically for web content, they can apply to PDF as well, with some slight adjustments.

But, due to limitations in current technology, some websites cannot reach AAA compliance. As such, the AA level is most commonly used, regardless of which version of WCAG is being used.

In addition, PDF/UA (the PDF standard for Universal Accessibility) and HHS (for The US Department of Health and Human Services) are other accessibility standards that, while less common, are frequently used.

So why are there so many options? How do I know where to start or what to use?

Do we need all these accessibility standards?

While compliance can sometimes feel like a moving target, standards serve as a detailed, uniform and consistent set of guidelines that help document creators guide their decisions. Even with a shared goal of document compliance, there are differences in requirements and best practices between these accessibility standards we’ve mentioned.

For example, it’s important to note that WCAG was developed for web content, so while the standard does apply well to PDF, it wasn’t its intended use. To put it plainly, not every checkpoint in WCAG will apply to PDF, and some even need to be “massaged” to be more PDF-related.

For example, HTML doesn’t have Lbl (label) tags in lists. As a result, WCAG technically doesn’t require Lbl tags in their lists, but the PDF/UA standard does. Also, decorative images are handled differently on a web page than in a PDF.

These are just a couple of examples of adjustments we make to make this web-based standard more relevant to PDF documents.

PDF/UA is PDF-specific and is considered the gold standard for accessibility in the PDF world.

HHS Guidelines

Some other notable standard differences can impact document creation. For example, historically HHS did not allow empty header cells in data tables, while WCAG and PDF/UA did. This led to slightly different table layouts based on the standard. HHS had specific requirements for file-naming conventions and required Bookmarks in nine pages or longer documents.

These requirements were unique to HHS — another indication that standard choice matters, and that standards change over time.

One of my favorite differences that has since been changed is that HHS used to have a set of six acceptable fonts that authors could use. This was very limiting in terms of document creation, but it is another example of different standards having notably different and unique requirements.

Given that standards are highly unique and sometimes a bit nit-picky, how do we decide which one to use?

Which accessibility standard to choose?

Unfortunately, that decision is either yours or a product of your surroundings. What I mean by this — is that WCAG 2.1AA is a commonly used accessibility standard, but it’s not right for everyone. In fact, the industry of the applicable document can play a huge role in choosing a standard.

For example, suppose you are a healthcare company. In that case, you might need to use HHS as your accessibility standard because your information falls under, or is most related to, the Department of Health and Human Services.

Some documents depend on the client.

If I am a marketing firm creating advertising materials for two clients, one might require PDF/UA for their website, and another might require WCAG.

Sometimes this choice is made at an organizational level, setting a precedent to take the guesswork out of future document creation and remediation.

Finally, since WCAG 2.1AA is so commonly used, many clients choose this option by default, but again, this might change once WCAG 2.2 becomes more widely adopted.

A Recommendation

Lastly, I want to leave you with a simple recommendation.

The only way to guarantee compliance is to ensure that your document is compliant against structural and accessibility standards. So, we at Allyant encourage all users to select one of each when running a document verification.

For some, this looks like ISO-32000-1 and one of the WCAG options, but for others, it could be ISO-32000-1 and PDF/UA.

There isn’t a single correct combination, but testing against both types of standards ensures that nothing falls through the cracks.

When running your verification, it is critical to address and correct all failures and manually verify all warnings and checkpoints that require user verification. Only then can you guarantee compliance and ensure your content is accessible to all audiences.