The file is a core data archive containing game assets like textures and sounds. When this file is "patched" or replaced, it is usually to fix the notorious "Server is different from the client" error or to resolve crashes that prevent the game from launching. The Role of .IWD Files in MW2
Your iw_22.iwd file must be located in the main folder of your game directory: ...\SteamLibrary\steamapps\common\Call of Duty Modern Warfare 2\main\iw_22.iwd call of duty modern warfare 2 iw 22iwd patched