How Do You Beat Doom 3 On Pc?

If your having trouble beating doom 3 then choose a lower difficulty level.If your still having problems, then use the following cheats:

First press Ctrl+Alt+~(Tilde) to bring up the command console in a single player game,then type following

clear lights - All lights turn off. Only light is by flashlight.
give all - All weapons with full ammo, health and armor
god - God Mode or invincible mode.
give ammo - Max Ammo