Ann,

            Are you asking about adding Alt Text for an image using Microsoft Word?  If so, it's a cinch, as it is under most HTML editors, too.

            If you're referring to something after the fact then it becomes significantly more complicated and murkier.

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Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763  

   Explanations exist; they have existed for all time; there is always a well-known solution to every human problem — neat, plausible, and wrong.

         ~ H.L. Mencken, AKA The Sage of Baltimore