Depending on how you own the game, you can retrieve your key through these methods: Steam Version Steam Library Right-click Arma 2: Reinforcements Operation Arrowhead if they are merged). Windows Registry
, which previously handled the series' multiplayer master servers. To preserve the game's community, Bohemia Interactive enabled the redemption of non-Steam retail keys on the
: You can still find individual keys for Arma 2: Operation Arrowhead or the specific DLCs at stores like Play-Asia or PremiumCDKeys. How to Activate Your CD Key on Steam
Unlocking the Full Tactical Experience with an Arma 2: Reinforcements CD Key