A family of Microsoft word processing software products for creating web, email, and print documents.
Start Word (or Excel). Which accounts / e-mail addresses are listed at File > Account? The important thing is which account licenses the subscription (the far right of the File > Account screen). See also Diana's reply.
Check the same list of accounts that is shown if you click your avatar at the top right of the status bar. See the screen shot below.
Generally, you would want to keep both lists to a minimum.