This is not uncommon but we need more information:

https://makemusic.zendesk.com/hc/en-us/community/posts/215729367-General-Discussion-House-Rules

Files created in 2003 on Finale 2001d were later sucessfully transferred to Print Music.  Worked on extensively and now required to be opened in the old Finale program  2001 for ongoing collaboration.  Can you help?

Although the stock answer that we need more information does apply, I know of no way to make newer Finale files open in versions that old except, possibly MusicXML. I still have my copy of 2001 installed on a G4 but I’ve not looked at it in years.

The only reference I can find is this one referring to a converter for Windows and Finale 2000–2002. I know of nothing for the Mac and you’ve not mentioned your OS. 

https://www.musicxml.com/publications/makemusic-recordare/xml-2001/musicxmls-approach-to-music-interchange/ 

I have no idea if this converter is still available nor what OS it may support—nor what features are backward compatible.

Really, the solution is to upgrade. PrintMusic is no longer available for Mac but is for Windows. Older licenses of Finale can be upgraded, however.