The BFG Edition features enhanced graphics, better audio with more horror effects, a checkpoint save system, and support for 3D displays and HMDs. The game also includes the previous expansion Resurrection of Evil and a new single-player expansion pack called The Lost Mission. Additionally, it includes copies of the original Doom (the Ultimate Doom edition with the add-on fourth episode, "Thy Flesh Consumed"), and Doom II with the expansion No Rest for the Living, previously available for the Xbox 360. The BFG Edition also features the ability to use the flashlight while holding a weapon, in the form of the so-called armor-mounted flashlight.Go to: http://store.steampowered.com/ and download STEAM client
Click “Install Steam” (from the upper right corner)
Install and start application, login with your Account name and Password (create one if you don’t have).
Please follow these instructions to activate a new retail purchase on Steam:
Launch Steam and log into your Steam account.
Click the Games Menu.
Choose Activate a Product on Steam…
Follow the onscreen instructions to complete the process.
After successful code verification go to the “MY GAMES” tab and start downloading.