If you are using the Microsoft PDF button, Save as PDF or the Export function to make a PDF – watch out!
The latest update, as of September 14, 2021, has changed and now the Alt text you provided inside a Word document is dropped and replace with gibberish code when exporting to a PDF.
For now, the temporary fix is to use the SAVE AS function and select the PDF (*.pdf) as the file type. Be sure to review the Options and activate the “Create bookmarks using:” function.
Sorry to say you will need to review the options menu for the settings each time. Always be sure to review your Alt text in Acrobat Professional.
Not sure when exactly this will be fixed – it is being worked on but it could take a while.