How do I change the resolution in Doom 3?

The file is called "DoomConfig.cfg". You have to put it in custom mode once it's found under "C:Program Files (x86)DOOM 3base"). Find out if it says "r_mode" and change it to "r_mode-1" Find the "r_customHeight" and the "r_customWidth". You should change it to your resolution. Start the game with "r_customHeight1080".