How to Activate: To activate codes in Doom, bring down the Command Console by pressing [Ctrl + Alt + ~]. Input the code you want to use, and then press Enter to activate it.
Obviously, since these codes do change the way the game is played, we suggest completing the game all the way through without the use of any command codes, and then experimenting with which codes work best for you on your subsequent playthroughs.
Console Commands
iddqd
Toggles God-mode (still damageable by hazards). Causes Health to drain slowly at all times on Nightmare Difficulty.
idkfa
Gives the Doom Marine fully upgraded Health, Armor, and Ammo Capacity, as well as all unlockable Weapons, Weapon Mods (all fully upgraded), Suit Mods, and all available Suit Mod slots.
idfa
Gives player fully upgraded Armor, Health, and Ammo Capacity.
idka
Gives player all Weapon Mods, Weapons, and Weapon Mods are all fully upgraded.
ida
Gives the Doom Marine all Suit Mods and all Suit Mod slots.
iddt
Reveal all Secrets, items, and any unexplored areas of the map.
idgk
Toggle Glory Kills only. Makes all enemies immune to firearms and normal weapons, requiring player to kill them with Glory Kill animations.