Manual Replacement (if you have a DLL):
The steamapi.dll file is a core component of Steamworks, Valve’s suite of tools for developers. When Crystal Dynamics built Tomb Raider (2013), they integrated SteamAPI to handle:
If Windows cannot find this file when you launch TombRaider.exe, your game will crash immediately or display an error like:
If the above steps don't resolve your issue, and you're specifically looking to download steam_api.dll for verification purposes (not recommended):