Alt text for figures in InDesign not reading aloud when PDF is opened in a web browser

@James Gifford—NitroPress is correct: I don't know of any browser that is fully compliant with the PDF/UA standard for accessibility. Reading Alt Text, changing language pronunciation, filling in form fields and a whole lot more features won't be found in browsers at this time. Maybe in the future, but there's nothing requiring them to become compliant.

True testing can only be done with a combination of compliant software and assistive technologies:

• JAWS and NVDA screen readers while in Adobe Acrobat Pro, Standard, or Reader.
• Any other combination will be hit and miss.

Using Adobe InDesign 24, I've set alt text for my figures using Object Export Options (repeated in both the Alt Text and Tagged PDF tabs).

By @Mary @ RockHarbor.biz

Just in the Alt Text tab. Skip the middle Tagged PDF tab for Alt Text.

Not all PDF readers are the same, by a long shot. Acrobat is the official tool and the only fully standards-compliant one; if something does not work in Acrobat Reader or Pro, there is likely a fault with the file itself.

However, all third-party readers and PDF tools, and especially those embedded in browsers, are often lacking the full feature set or a faultless implementation of features they do have. Very few "advanced" features like forms, interactivity, animation or accessibility are well-supported in either mobile or web readers.

There is no solution except to have users use Acrobat (and I am not sure the browser plugin is as fully-featured as the app, at that.)

But if there's a fix, I'd bet @Bevi Chagnon - PubCom.com knows what it is.