First, if you have an older version of Microsoft Office, even as old as the 2000 version, keep it. You are very unlikely to find any functional difference of value in more recent versions and the software runs quite well on Windows 7.
I advise my clients to always decline the offer to add Microsoft Office to their new computer purchase. There are several reasons:
- Price is usually just about the same as a retail purchase
- OEMs seldom provide the Product key for pre-installed Office
- Microsoft will not provide support for Office when it was pre-installed. They send you to the OEM
- Retail versions of Office are portable. They can be installed in any ONE PC. OEM versions are tied to that PC.
Buying the retail version is going to be far more economical in almost all circumstances than “renting” it like in Office 365.