Captions and PDFsMaking PDFs, documents, video and audio work for everyone
Chapters (8)
  1. Why PDFs, documents and media need their own care
  2. Making a PDF accessible with tags, reading order and bookmarks
  3. Building Word files that turn into good PDFs
  4. Slide decks that turn into good PDFs
  5. Captions, subtitles and transcripts: what's the difference?
  6. When does a video need audio description?
  7. How to check a PDF for accessibility problems
  8. How to check a video or podcast for accessibility

Why PDFs, documents and media need their own care

Last reviewed

Quick take

  • A web page has built-in structure. A PDF, a Word file or a video often doesn't.
  • Documents need structure that software can read: headings, order and tags.
  • Recorded media needs text versions: captions, transcripts and descriptions.
  • Fixing the file at the start is much easier than repairing it later.

Your web page may be fine, and the file may not

Say your site has a clean "Opening hours" page. Then you add a PDF menu. The page works with a screen reader. The PDF might not.

A screen reader is software that reads a screen out loud, or sends it to a braille display. It needs a file to say what each part is. A heading, a list and a table all need a label that software can find.

Downloads don't always carry those labels. And videos and recordings bring a different problem: some people can't hear them, and some can't see them.

Two panels. Documents: PDF, Word and slides, which need structure such as headings, order and tags. Media: video and audio, which need text versions such as captions and transcripts.
Documents need structure. Media needs text versions.

Documents: the order can go wrong

A PDF can look perfect and still be a jumble to a screen reader. The meaning sits in a hidden layer called tags. Tags are labels that say "this is a heading" or "this is a table". That hidden layer is created when a document is saved as a tagged PDF.[1]

Order is the clearest example. Picture a page with two columns. You read down the first, then down the second. A screen reader with no tags may read across both columns as if they were one.[1] The words come out mixed up.

Two page sketches with six numbered blocks in two columns. On the left the numbers run down column one and then column two. On the right they run straight across the rows, which mixes the columns up.
Why order matters: the same page can be read in a good or a bad order.

When the order is wrong, people using keyboards or assistive technology may not understand the content at all.[1] The next page, making a PDF accessible, shows how tags and order are set.

Media: sound and picture need words

A video has two channels. If a person can't hear, they miss the sound. If a person can't see, they miss the picture.

Captions fix the first problem. They are a text version of the speech and of the other sounds a viewer needs.[2] Audio description fixes the second. It tells blind viewers what is shown on screen.[3]

Neither one comes for free. Someone has to write them. The pages in the Video and audio section show how.

Ask first: does it need to be a file?

Sometimes the best fix is no file at all. One U.S. government guide says PDFs are often not the most accessible or mobile-friendly option.[4] Ask whether a plain web page would do the job.

A question box: could this be a web page? Yes leads to use a web page, which is often easier. No leads to make an accessible PDF.
A web page is often the easier choice.

If you do need the file, build it well from the first draft. Start with Word files that convert well.

Sources

  1. PDF3: Ensuring correct tab and reading order in PDF documents, W3C Web Accessibility Initiative (accessed 2026-11-10)
  2. Captions/Subtitles, W3C Web Accessibility Initiative (accessed 2026-11-10)
  3. Description of Visual Information, W3C Web Accessibility Initiative (accessed 2026-11-10)
  4. Create Accessible PDFs, Section508.gov (U.S. General Services Administration) (accessed 2026-11-10)