What Can a PDF Accessibility Checker Actually Detect?

You run your PDF through an accessibility checker and get a passing result.

Does that mean the PDF is accessible?

Not necessarily.

Automated PDF accessibility checkers are useful tools, but they have limits. They can quickly and consistently identify many technical issues, making them an important part of an accessibility workflow. But they cannot evaluate every aspect of a PDF’s accessibility, especially when accessibility depends on context, meaning, or whether the document’s structure actually makes sense to a person using assistive technology.

Understanding what a checker can and cannot detect can help you use automated testing more effectively and avoid treating a passing result as the finish line.

What Does a PDF Accessibility Checker Check?

Most automated PDF accessibility checkers look for specific technical conditions that can be evaluated against defined rules.

Depending on the checker, it may identify issues such as:

• Missing or incomplete tags
• Untagged content
• Missing document language
• Missing title or metadata
• Missing alternative text
• Certain heading structure issues
• Problems with lists
• Certain table structure problems
• Form field issues
• Link and annotation problems

These automated checks are valuable because they can evaluate a document much faster than a person could manually inspect every element.

For organizations with large PDF libraries, that efficiency matters. Automated testing can help identify potential problems, prioritize documents for remediation, and catch technical issues consistently.

But there is an important distinction:

A checker can determine whether certain accessibility requirements appear to be present. It cannot always determine whether those requirements are implemented correctly or whether the document is actually usable.

What an Accessibility Checker Can’t Fully Evaluate

Many accessibility questions aren’t simply yes-or-no technical questions.

For example, a checker may be able to determine that an image has alternative text. But can it determine whether that alternative text communicates the important information contained in the image?

It may be able to identify headings. But can it determine whether the headings accurately represent the document’s hierarchy?

It may be able to identify a tagged table. But can it understand whether a person using a screen reader can make sense of the relationships between the headers and data?

These questions require context.

That’s where automated testing has limitations.

A Passing Result Doesn’t Mean the Reading Order Is Logical

Reading order is a good example of something that can be difficult to evaluate automatically.

A PDF can contain tags and still present content in an illogical sequence.

This is especially common in documents with:

• Multiple columns
• Sidebars
• Text boxes
• Headers and footers
• Captions
• Pull quotes
• Complex layouts

A checker may be able to verify that content has been tagged. It may not be able to determine whether a screen reader will encounter that content in the order a person is expected to read it.

The document might look perfectly organized visually while its underlying structure tells a very different story.

A Checker Can Find Missing Alt Text, But Not Always Bad Alt Text

Automated testing can often answer a straightforward question:

Does this image have alternative text?

The harder question is:

Is the alternative text useful?

Consider an image of a chart showing the organization’s annual budget.

Alt text that says “budget chart” technically identifies the image. But it may not communicate the information the chart is intended to convey.

Likewise, an image with alt text such as “image” technically has alternative text, but that description provides little value to someone who cannot see the image.

Determining whether alternative text communicates the right information requires an understanding of the image and its role in the document.

A checker can help identify missing alt text. It cannot reliably determine whether the description is meaningful in context.

Tags Don’t Automatically Mean Good Structure

Tags are fundamental to PDF accessibility because they provide structure that assistive technology can use.

But having tags isn’t the same as having a well-structured document.

A PDF might contain heading, paragraph, list, and table tags while still having structural problems.

For example, a long report might contain headings that are tagged correctly from a technical standpoint but don’t create a logical hierarchy for navigating the document.

The important question isn’t simply:

Are there tags?

It’s:

Do the tags accurately represent the document’s structure and relationships?

That distinction is easy to miss when accessibility is treated as a checklist of technical requirements.

Tables Can Be Technically Correct but Practically Difficult

Tables are another area where automated testing has limitations.

A checker may identify whether a table has header cells or whether certain table structures are present. But complex tables can contain relationships that are difficult to evaluate without understanding the information being presented.

For example, a table might contain:

• Multiple levels of headers
• Merged or spanning cells
• Subcategories
• Repeated headers
• Blank cells with meaning
• Relationships between rows and columns that aren’t obvious from the underlying structure

A sighted reader can often understand those relationships from the visual presentation.

A screen reader needs those relationships to be represented in the PDF’s underlying structure.

Automated testing can help identify technical problems, but human review may still be necessary to determine whether the table actually communicates its information effectively.

Forms Have Similar Limitations

The same principle applies to interactive PDF forms.

An automated checker may be able to identify whether form fields have labels or whether certain required properties are present.

But accessibility also depends on whether the fields are presented in a logical order and whether their labels make sense to the person completing the form.

A form can therefore pass individual technical checks while still providing a confusing experience.

Again, the issue is the difference between having the required elements and using those elements effectively.

So What Is an Accessibility Checker Good For?

The limitations of automated testing don’t make accessibility checkers unnecessary. Quite the opposite.

They make them useful for a different reason.

Automated checking is particularly valuable for finding technical issues efficiently and consistently.

For organizations managing large numbers of PDFs, manually inspecting every document for every possible issue would be extremely time-consuming. Automated tools can quickly identify potential problems and help remediation teams focus their attention where it is needed.

They can also provide a useful quality-control step after remediation, as long as you remember that passing the checker does not mean there is nothing left to evaluate.

What Should You Do After a PDF Passes?

Once a PDF passes automated checks, take a closer look at the areas that depend on human judgment.

Ask:

Does the content follow a logical reading order?

Do the headings create a meaningful hierarchy?

Does alternative text communicate the important information in images?

Are tables understandable when their structure is interpreted by assistive technology?

Are links and form fields meaningful and logically organized?

Does the document communicate the same information to someone who cannot see the visual layout?

These questions go beyond simply confirming that a particular technical requirement exists.

For more complex or high-priority documents, testing with assistive technology can provide another important layer of validation. A screen reader can reveal problems that aren’t obvious from an automated report or from looking at the PDF visually.

Automated Testing and Human Review Work Together

The choice doesn’t have to be between automation and manual testing.

The most effective approach uses each for what it does best.

Automated tools can identify technical issues quickly, consistently, and at a scale that would be difficult to achieve manually.

Human review can evaluate context, meaning, logical structure, and the actual usability of the document.

For organizations with large PDF libraries, this combination can make accessibility work much more manageable. Automation reduces the amount of manual work required, while human oversight helps ensure that remediation isn’t reduced to simply checking boxes.

How Equidox Helps

Equidox helps organizations move beyond simply identifying PDF accessibility issues. Its automated remediation tools can address many of the structural elements that require significant manual effort, including reading order, lists, tables, and other tagged content. Built-in HTML Preview provides another way to review the document’s underlying structure and how content is organized. Equidox combines automation with human oversight, giving organizations a way to remediate PDFs more efficiently while still reviewing the areas where context and judgment matter.

A Passing Checker Result Is a Starting Point, Not the Finish Line

PDF accessibility checkers are an important part of the remediation process. They can find many technical problems quickly and help organizations maintain more consistent accessibility workflows.

But accessibility is about more than passing a set of automated rules.

A PDF can have tags, alt text, headings, tables, and form fields and still present information in a way that is confusing or inaccessible.

Use automated testing to identify what can be checked automatically. Then look beyond the results to evaluate whether the document’s structure, content, and information actually work for the people who need to use it.

The goal isn’t simply to make a PDF pass a checker. The goal is to make the PDF accessible.

 

Nina Overdorff

Nina comes to Equidox with years of sales and marketing experience from a variety of industries and holds a BS in Language Arts Education. Nina has a passion for words, storytelling, and information, which she believes everyone should have access to regardless of ability. After spending time as a teacher with a blind student, she became much more aware of the limitations and abilities of web accessibility, and how essential it is to those experiencing disabilities. “Being able to access information equally ensures that everyone has an equal opportunity for education, employment, and success in life.”