How to add alt text to a PDF

Alternative text is what a screen reader says when it reaches an image. Getting it in place is mechanical. Writing a good one takes thirty seconds of judgment — and that is the part worth learning.

Where it goes

In Word, before you export

Right-click the image → View Alt Text → type the description in the panel. If the image carries no information — a decorative divider, a background flourish — tick Mark as decorative instead. That tells a screen reader to skip it silently, which is correct and much better than an empty description.

Then export with File → Save As → PDF → Options → "Document structure tags for accessibility." Printing to PDF discards every description you just wrote.

In Acrobat, on a finished PDF

All tools → Prepare for accessibility → Set alternate text. Acrobat walks through every image in the document one at a time, with a box for the description and a checkbox for decorative. For a document with a handful of images this takes a few minutes.

What to actually write

The rule is not "describe the image." It is "convey what the image conveys." The same photograph gets different alt text depending on why it is on the page.

The four cases you will actually hit

Decorative

A stock photo of a sunset next to a parks announcement, a divider line, a background texture. Mark as decorative. Do not describe it. A screen reader user does not need to hear about the sunset; they need to get to the announcement.

The seal, the logo, the letterhead

Write what it is, not what it looks like: City of Springfield seal. Not circular blue emblem with an eagle and a banner reading Founded 1847. Nobody needs the heraldry.

A chart or a graph — this is the one people get wrong

Do not describe the picture. State the finding.

If the chart is complex enough that a sentence cannot carry it, put the underlying numbers in a real table elsewhere in the document and let the alt text point to it.

A map or a site plan

These are genuinely hard. Describe the purpose and the answer, not the geography: Map showing the proposed rezoning area: the six parcels on the north side of Elm Street between 4th and 6th Avenue. If the map is the entire point of the document — a zoning map, a flood map — the honest answer is that alt text cannot substitute for it, and you should provide the same information another way: a list of affected addresses, a table of parcels, a phone number for someone who will read it out.

Length and phrasing

• Aim for one sentence. Two if the image is carrying real information.
• Skip "image of" and "picture of." The screen reader already announced that it is an image. Starting with those words wastes the listener's time on every single image.
• Don't repeat the caption. If a caption below the image already says it, mark the image decorative — otherwise the user hears the same thing twice.
• Include text that appears inside the image. A flyer saved as a picture is invisible to a screen reader; every word on it has to be in the description, or better, the flyer should not be an image in the first place.

A note on scanned documents

If someone scanned a paper flyer and posted it, the entire page is one image. Alt text is not the fix — you would be writing a description of an entire document. The real fix is to recreate it as a real document, or run text recognition and tag the result. Our checker flags this case specifically, because it is common and because it is the one that leaves a reader with literally nothing.