Office 2008 is “finished” because Office 2008 is 32-bit software, and 32-bit software can no longer run on the post-Mojave builds of macOS. (Meanwhile, on the Microsoft side, they stopped supporting it and Office 2008’s updates quite some time ago). There’s the option of buying a licence for the latest version of Office for Mac, which will have its own “code” (serial), or as
@velocityg4 noted, an open-source office software set like LibreOffice.