DLC for EU4 that turn your game into "digital extreme edition" or w/e. Please check if you own it among your Steam licences (it doesn't show among owned dlcs in library or store).

-> you can see it as either Europa Universalis IV Extreme Edition (game+dlc pack) or Europa Universalis IV: Digital Extreme Edition Upgrade Pack (just dlc).

Key will be shown on your 'won' page. Good luck! :)