每次打開OFFICE軟體一直出現認證選項

For one-time purchase versions of Office, each license can only be used on one PC/Mac, and when several one-time licenses are under the same Microsoft account, using the wrong install/license can cause activation prompts. Microsoft recommends signing in with the account used to buy/redeem Office, and activating by signing in rather than entering the key again, and ensuring no one else is using the same activation on a different device, as this will cause you to get this prompt next time you open the app.

Please try this on the affected computer: close all Office apps, then go to Control Panel > Programs and Features and check if more than one Microsoft Office/Microsoft 365 version is installed. If there is a trial/preinstalled Office version plus your paid Office version, uninstall the unused one. Then open Word > File > Account, sign out of all accounts, close Office again, restart the PC, and sign back in with the Microsoft account that owns the license.