In the world of the id Tech 4 engine, files are essentially renamed .zip archives. They act as "containers" that hold every asset used to bring the game to life. If you were to open one with a program like 7-Zip or WinRAR, you’d find: Maps: The structural layout of the levels. Textures: The grimy, metallic surfaces of the Mars base. Sounds: The terrifying whispers and industrial hums.