Adding Alt Text to PDFs for Better Accessibility

Alt text is a short written description of an image or graphic.

In PDFs, it helps screen reader users understand meaningful visuals such as:

Charts
Diagrams
Photos
Icons with meaning
Infographics

If an image adds information, it should usually have alt text. This is one part of creating an accessible PDF, especially when visuals carry meaning.

Why Alt Text Matters

Not everyone can see the image.

Alt text helps explain what the image means instead of just what it looks like.

That improves:

Screen reader support
Document comprehension
Accessibility compliance
Usability for more readers

It is one of the simplest ways to make a PDF better. W3C’s tutorial on informative images is a helpful neutral reference for deciding what an image needs to communicate.

When Alt Text Is Needed

Alt text is usually helpful when the image carries meaning.

Examples include:

A chart showing sales trends
A photo illustrating a process
A diagram explaining a workflow
An icon used as a button or label

If the image is only decorative, it may not need alt text. W3C also explains how decorative images should be handled so they do not add clutter for screen reader users.

Write Clear Alt Text

Good alt text should be short, specific, and useful.

Try to:

Say what the image communicates
Avoid repeating surrounding text
Keep the description concise
Focus on the important point

The goal is to help the reader understand the content, not overload them with detail.

Add Alt Text in the Source File

The best place to add alt text is usually the source document before export.

That way:

The structure is preserved
The PDF export can carry the information forward
The source remains easier to maintain

If you only edit the PDF later, not every tool will support full accessibility tagging. For broader remediation work, this guide on how to fix PDF accessibility with AI covers the kinds of checks that may still be needed.

Check the Final PDF

After export, test whether the alt text is still present and usable.

Check:

Whether the image is tagged properly
Whether the reading order still makes sense
Whether screen reader tools can identify the description
Whether decorative images were left unlabeled intentionally

Accessibility should be tested, not assumed. If the PDF is based on scanned images, you may also need OCR; this guide to making a PDF searchable explains that related step.

Common Mistakes

Alt text can go wrong when:

The description is too vague
The text repeats the caption word for word
Decorative images are given unnecessary descriptions
Important images are left without any description
The PDF export strips the tagging

Good structure and review solve most of these problems.

Best Practice Summary

If you want the short version:

Add alt text for meaningful images
Keep the description short and useful
Add it in the source file when possible
Test the final PDF with accessibility tools
Leave decorative images unlabeled when appropriate

That is the simplest way to add alt text to PDFs for better accessibility.

FAQ

What is alt text in a PDF?

It is a short description that helps explain an image to assistive technology.

Do all images need alt text?

No. Decorative images may not need descriptions.

Should alt text be long?

Usually no. It should be concise and useful.

Can I add alt text after the PDF is made?

Sometimes yes, but the source file is usually the better place to add it.

Why is alt text important?

It helps people understand meaningful images without seeing them.

Does alt text help screen readers?

Yes. That is one of its main purposes.