Catalina/MS 2008

You can open Numbers or Pages, then I believe you go to the File pull down menu and click on Open. Select which file you want to open, then click in it in the window. You can the work on the file as needed, then do the normal Save function. The file will then have a Pages or Numbers icon. If you need to send one of these files to someone else, I believe the process would then be to do a save as command and select Word (or Excel).

macOS Catalina only supports 64-bit apps.

Older 32-bit apps, like older versions of Microsoft Office, might need to be updated to function properly with macOS Catalina.