Bad Piggies was originally released by as both a free-to-play mobile app and a paid PC version that required an activation key. However, Rovio officially discontinued the PC version years ago.
The Search for a Bad Piggies Full Game Activation Key: Truth, Risks, and Legitimate Alternatives Bad Piggies Full Game Activation Key
Even on legitimate key reselling marketplaces (like G2A or Kinguin), keys for older Rovio games are rare. If you do find one, it may be: Bad Piggies was originally released by as both