Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
If the Office product key was already redeemed, it is no longer needed for reinstalling or activating Office. Use the Microsoft account that was used to buy or redeem Office:
- Go to Services & subscriptions.
- Sign in with the Microsoft account used for the Office purchase.
- Install Office from there.
- If an Office app asks for activation, sign in with that same Microsoft account instead of entering a product key.
If the product key was never redeemed and is lost or damaged, Microsoft support may be able to help if valid proof of purchase is available. Contact Microsoft support.
If the product key does not work, contact the seller and request a refund. Microsoft notes that keys sold separately from software are often stolen or unauthorized and can be blocked.
If Office came preinstalled on a new PC, there may not be a printed key. In that case, either a digital product key was transmitted to the PC during Windows activation, or the preinstalled Office was only a trial.
References: