You can purchase and download the game legally through the following platforms: Official Platforms & Pricing :
: Prices typically match Steam, with the Zombies Chronicles Edition often listed at $59.99. Amazon : Offers digital codes and physical copies for PC. Potential Savings
: ~$14.99 (Limited multiplayer-only version).
If you are looking for a lower price point, consider these options: Call of Duty®: Warzone™ on Steam
Call of Duty: Black Ops III is from official sources . While some newer titles in the franchise like Call of Duty: Warzone are free-to-play, Black Ops III remains a paid title.