Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
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Each Microsoft Office product is licensed via the associated Microsoft account. Reactivation may be required, for example if major hardware components have been replaced in the PC. This may be problematic for a version which was preinstalled by the computer manufacturer, if you haven't been given access to the account (or if the license is OEM). You can check with the manufacturer's support site if there is a simple solution. Unfortunately, with a ten year old PC, you may not get any assistance from the computer manufacturer. The end result under these circumstances is that you may have a license that you just can't access.
You can use an open source alternative such as LibreOffice. File compatibility with the Microsoft Office file formats is rather good.