With pre-orders of this title.
The Microsoft Windows PC version of Doom (2016) releases tomorrow (May 12, 2016), which means that today is your last chance to receive a pre-order incentive with that title.
Green Man Gaming and Gamersgate are offering a free copy of Doom 3: BFG Edition for free if you pre-order Doom (2016); while Steam are offering a free copy of Wolfstein: The Old Blood.
Both Doom 3: BFG Edition and Wolfstein: The Old Blood normally sells for $19.99.
Please note that in general, the PC version of Doom (2016) requires a free Steam account to activate and play.