AC7 (which also is available in an OSX version that even runs fine on MacIntels) should open anything as far back as AC4.5, I think.
You should be able to get a copy of AC7 from your reseller if you have a current licence. It runs with current WIBU keys.
Hopefully your file is a .pla which contains the library objects needed. Otherwise, you might get problems with any non-standard items.
Open in AC7, Save As (new name.pla) - this should make the file AC7-native.
Then Open in AC9, Save As (new name again.pln) - this should make it AC9-native.
Then Open iin AC10 or 11. Save As again.
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1