There is no CD key for "Doom 3"; however, a technical issue causes the game to ask the player to enter such a key the first time it is launched. While launching the companion game, "Doom 3: Resurrection of Evil," bypasses this issue for many, others find it necessary to contact Steam technical support.
A technical glitch exists in game packages containing both "Doom 3" and "Doom 3: Resurrection of Evil," in which players are asked to enter a CD key when initially launching "Doom 3." No CD key is required to play this game after purchase. Experts have advised players to launch "Doom 3: Resurrection of Evil" initially, then return to "Doom 3." This often resolves the issue and allows continued play without the CD key. In the event the issue persists, contact technical support for instructions on installing a patch.