You haven't posted platform, version info etc in your signature.
On the Mac at least a document double-clicked always opens in the last installed or updated program version. In your case, 8.1 has got that label from the O/S.
You could uninstall 8.1. Or re-install the latest version (insert CD and Repair would do, maybe). Perhaps just installing the latest hotfix will do it.
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1