You need a CD/DVD drive. But you can usually take the paper key and redeem it directly in Steam (the game was a "Steamworks" title).
Since the official servers are dead, the community has developed several methods to bypass the activation screen: bad piggies pc activation key
$15–$40 for a sealed box.
A few years after release, Rovio officially shut down its PC games shop. They discontinued direct support, updates, and key verification servers for the legacy Windows versions of Angry Birds and Bad Piggies . You need a CD/DVD drive