The Arma 2 Reinforcements CD key is a unique code that grants access to the Reinforcements expansion pack for Arma 2. This expansion adds a significant amount of new content to the game, including new missions, vehicles, and game modes. The CD key is a 20-character code that is used to activate the expansion pack and unlock its features.

Depending on where you bought the game, you can find the key in the following locations: Windows Registry