Use the same Microsoft account you use for Microsoft Office.
If you’re getting the add-in from the Office Store on the web, you’ll have to first click the “Add” button on the add-in’s page and sign in with your Microsoft account, if you haven’t already. If you opened the Office Store pane from within a Microsoft Office application, the add-in will immediately appear in a sidebar at the side of your office document.
Once you’ve found an add-in you like, click the add-in and click “Trust It” to give the add-in access to the contents of any document you use the add-in with. This provides you with a complete list of add-ins available for all Office applications. You can also visit the Office Store website online.
