Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Office 2021 remains a one-time-purchase license, so first reconnect the installed apps to the Microsoft account that owns Office 2021; purchasing Microsoft 365 should not be necessary.^1^
Try this first—no reinstall
- Open Word or Excel.
- Check the displayed product:
- Windows: File → Account → Product Information
- Mac: menu bar Word/Excel → About Word/Excel
- Sign out of any work, school, or unfamiliar Microsoft 365 account.
- Sign back in with the personal Microsoft account used to redeem or purchase Office 2021.
- Close every Office app, reopen Word, and check whether saving works.
An activation failure puts Office into reduced-functionality mode and disables most features. Microsoft’s first prescribed check is therefore the account associated with the purchase.^2^
To identify the correct account, open the Services & subscriptions page:
https://account.microsoft.com/services
Sign in with each personal Microsoft account that might have been used in 2022. The correct one should list Office Home & Student 2021, Office Home & Business 2021, or another Office 2021 product. If Office 2021 is absent, that address cannot activate this purchase.^2^
Do not redeem the original key again if it was already redeemed. A redeemed key becomes associated with the Microsoft account, which is then used for later activation or installation.^3^
If this is a Mac
If the message says “We’ve detected a one-time purchase license”
That exact message indicates that the Office apps came from the Mac App Store. Those copies require Microsoft 365 for editing and are incompatible with one-time Office licenses. The compatible apps must be downloaded directly from Microsoft.^4^
Unfortunately, that specific condition cannot be corrected only by dismissing the Microsoft 365 screen:
- Close Word, Excel, PowerPoint, and Outlook.
- Open Finder → Applications.
- Control-click each Office application and choose Move to Trash. This removes the applications, not personal documents.
- Download the Office 2021 for Mac Installer directly from Microsoft: https://go.microsoft.com/fwlink/?linkid=2158744
- Run the package, open Word, and sign in with the account showing the Office 2021 purchase.
If the apps are already Microsoft-downloaded copies
Reset only the Mac licensing information before considering reinstallation:
- Confirm that the Office 2021 purchase appears in the account page and that the password works.
- Quit every Office application.
- Download and run Microsoft’s Office License Removal Tool: https://go.microsoft.com/fwlink/?linkid=849815
- Open Word and sign in with the account associated with the one-time Office 2021 purchase.
- If offered multiple licenses, select the one-time-purchase Office 2021 license.
- Restart the Mac.
The tool removes all local Office licenses, not documents, and requires the purchase account credentials for reactivation.^5^
If this is Windows
If signing into the correct account does not reactivate Office:
- Open Control Panel → Programs → Programs and Features.
- Search the list for Office.
- If multiple editions appear, remove only the unused Microsoft 365 trial or duplicate edition, then restart Windows.
- Open Word and sign in with the Office 2021 purchase account.
- If only one installation exists, select it and use Change → Online Repair, then reopen Word.
Multiple installed Office editions can conflict with activation; Microsoft recommends removing the unused copy and repairing the remaining installation if necessary.^2^
Office 2021 lifecycle
Office 2021 support ended on October 13, 2026, meaning it no longer receives technical support, bug fixes, or security updates. End of support does not automatically revoke the perpetual license: Microsoft states that the applications may continue to function.^6^ Activation still requires occasional Internet access to confirm the license associated with the device.^1^
References
- Office 2021 and Office LTSC for Windows and Mac FAQ | Microsoft Support
- Unlicensed Product and activation errors in Office | Microsoft Support
- Where to enter your Office product key | Microsoft Support
- Microsoft Office activation and the Mac App Store | Microsoft Support
- How to remove Office license files on a Mac | Microsoft Support
- End of support for Office 2021 | Microsoft Support