If you have a legacy copy of the game on PC, you might encounter a screen asking for a full version activation key. Historically, these keys were used to unlock the full experience after playing the demo.
Angry Birds Space was released on Steam for Windows briefly. That version is the full game. While you cannot buy it directly anymore, you can purchase for the game from third-party resellers. These keys are safer than mobile keys because Steam’s redemption system still works. Angry Birds Space Full Game Activation Key