Typically, the game is installed in a directory like C:\Program Files (x86)\Steam\steamapps\common\Hearts of Iron IV for Steam users. For cracked versions, it might be in a folder like C:\Games\Hearts of Iron IV .
Invalid .mod file. Open your .mod file in Notepad. Remove any line that says archive="... . That is for Steam compression and breaks cracked versions. how to install mods for cracked hoi4