Ray Dream files can have extensions .RD4 for version 4 and .RDS.
Corel licensed the software around 1996 and bundled Corel Dream3D with its CorelDRAW suite, starting with version 6. Corel Dream3D files have the .D3D. extension but are the same file format. Carrara files use the extension .CAR, but are also the same format.
All files have the header "
33444320" or "3DC " in ascii. Followed by the software and version which produced the file. ie. "Ray Dream Designer(R) 3.0" or "Ray Dream Studio(TM) 5"