From the manual.
Gamestudio uses several proprietary file formats that are similar to popular formats used by other engines, such as the engines by id Software. There are five Gamestudio-specific file formats: WMP for a level, WAD for level textures, WMB for a compiled level with BSP tree and lightmaps, MDL for animated models, and HMP for terrain.

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WMB files are created by WED's Map Compiler. They contain the content of the WMP file with included textures, BSP tree data, and lightmaps.

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