If you manage multiple seats:
CATIA V5 R21 was written for Windows 7. To keep it "verified" on a modern OS, you need specific tweaks that do not violate the integrity of the software: catia v5 r21 verified
One of the most important "verified" utilities in R21 is managing files for users on older releases (like R20). The Utility : Navigate to Tools > Utility and double-click on Downward Compatibility Conversion If you manage multiple seats: CATIA V5 R21