Instead of downloading the file from a third-party site—which can be unsafe—try these official methods: Open your Steam Library and right-click on the game. Select Properties > Installed Files (or Local Files).

The filename itself is a roadmap:

If you are playing the newer engine (IW 8.0), the file structure has changed slightly, but the principle remains.

: Its primary purpose is to tell the game how to handle textures, shadows, and resolution.