Digital Archives: Some legacy software repositories archive older versions of Office. If you use these, ensure you are downloading from a reputable source to avoid malware.
If you'd like, I can help you find more specific resources for your Mac by knowing: Is your Mac an ? How much RAM does it currently have?
For the best experience on Mac OS X Lion 10.7.5 in 2021, seek out a copy of Microsoft Office for Mac 2011 Home & Business. It provides the best balance of modern file compatibility and "period-accurate" performance for your Mac.
No Security Patches: Neither OS X Lion nor Office 2011 receive security updates. Avoid opening email attachments from unknown sources.
Requirements: You will need a browser that still works on Lion, such as a late version of Waterfox Classic or Pale Moon (Safari on Lion is too old to render modern websites). Pros: It is free and always up to date.