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Avery Hymel

What are the Differences and Similarities Between Structural and Accessibility Standards in Digital Documents?

Scope of this article:

  • The Structural check tests against the PDF creation standard, ISO 32000. While ISO 32000 mentions accessibility functionality in PDF, it is broader.
  • The Structural check confirms if the PDF is built correctly, verifying links, forms, graphics, and PDF encoding. (This is not the same thing as character encoding, although that’s a thing, too.)
  • The Accessibility standards approach the broader concept of what’s allowed in a PDF and tighten that up for accessibility.
  • We often refer to WCAG (Web Content Accessibility Guidelines) 2.1 regarding accessibility standards because it’s so widely used.
  • WCAG 2.0 is ISO standard 40500. There is no update to the ISO standard, and there is no new ISO standard for WCAG 2.1.
  • It is important to note that WCAG is for the web and not PDFs.
  • Sometimes WCAG wants you to do something to your webpage that isn’t supported in PDF.
  • Occasionally, the PDF specifications will require you to do things differently because it is not web technology (like links in PDFs needing Alt text/Contents). Contents are a properties field for Link Annotations. It is a formal name for a descriptor that the standard calls for. (Alt text, Actual text, Expansion Text, Contents, Tooltips, Language – are some similar properties.
  • The PDF/UA spec – ISO 14289 – is the accessibility standard specific to PDF. So, it takes what is allowed in a PDF and reins that in for accessibility.

Running a standard check may be the most essential step for document accessibility. For this reason, we spend a great deal of time and energy remediating a document to comply with and pass the standards.

Structural check vs. accessibility check

There are two major types of standards, and as a result, we recommend testing all documents against structural and accessibility standards to guarantee usability, accessibility, and overall compliance.

In short, a structural check tests issues with the actual assembly of a document. In contrast, an accessibility check verifies that the PDF is accessible to all audiences.

For example, in the case of an image or graphic, a structural check confirms that fonts are encoded correctly and mapped to Unicode. Likewise, an accessibility check ensures that the text is tagged correctly.

Both are extremely important. The structural check verifies the correct content encoding. The accessibility check verifies proper tagging so that assistive technologies can handle it accurately.

ISO 32000

To get more specific, the structural standard checks against ISO 32000, which is the unofficial guide to making a PDF. ISO 32000 addresses some accessibility functionality, but its primary purpose is to ensure correct PDF construction. ISO 32000 offers guidelines for software developers and content authors. It checks document components like links, forms, graphics, and the literal encoding of the PDF.

PDFs currently aim for compliance against only one structural standard, ISO-32000-1 (version 1). Once PDF supports them, more up-to-date options like version 2 (ISO 32000-2) will be available.

Accessibility standards

Accessibility standards are a bit more specific. First, you’ll notice that I said standards – plural. There are many of them! Some relate to specific industries, and some are updated versions of previous accessibility standards.

The US Department of Health and Human Services developed the HHS standard for healthcare organizations.

The original Section 508 standard was updated to incorporate, by reference, WCAG 2.0. And WCAG 2.0 has since been updated to WCAG 2.1. So while we recommend clients check against ISO-32000, accessibility standard selection is based on multiple variables, like the needs of your particular organization.

Compared to structural standards, accessibility standards take a broader approach to what’s allowed in a PDF and make it more specific.


While both of our standard types consider accessibility, the accessibility standards are all about access. We often refer to WCAG 2.1 when referencing accessibility standards because it is the most widely used. The older version of this standard, WCAG 2.0, has become the ISO standard 40500.

There is no published ISO standard for WCAG 2.1, although we believe it’s in the works. It may be published as an updated version of ISO 40500 or a whole new ISO specification. We’ll have to wait and see.

WCAG, or the Web Content Accessibility Guidelines, are technically for web content. However, the technology that goes into web content creation and accessibility differs from PDF accessibility.

WCAG functionality does not always work with PDFs. Sometimes, the opposite is true. For example, links require alternative text in the PDF specification, but that functionality does not function similarly for web-based links.


PDF/UA (the “UA” stands for Universal Accessibility), another accessibility standard frequently referred to as the gold standard for PDF accessibility, is ISO 14289. This accessibility standard is specific to PDF. It takes the general idea of what is allowed in a PDF and focuses on accessibility.

Again, our general recommendation is to check documents against both structural and accessibility standards. That can look slightly different, depending on what accessibility standard you want to meet, but the goals are the same.

Complying with both standard types helps confirm that your PDFs are built appropriately and are accessible to all audiences.