A RAR file (Roshal Archive) is a compressed data container that holds one or more files. It is used to:

: Modders often package several textures or scripts into a single archive for easier distribution.

The specific dt07 file often serves as the container for the game engine. Downloading a dt07.rar usually implies you are acquiring a "patch" or "mod" intended to:

: Correct graphical glitches found in the base game's environments.