I know that there's the possibility to convert parts with the feature 'DownwardCompatibility' but i really have some problems with that...
So i try now to invert the whole thing and i just want to know if it's possible to open parts in catia v5r21 which were made in v5r20?
yeah you can centainly open R20 parts in R21
Yes. Should be ok. Would not work in the opposite direction though - would not be able to open a part in V5R20 that was created or edited in V5R21.
Yes it is possible.. But its not the other way round.