Sometimes legitimate game files are wrongly quarantined. Users should check their antivirus quarantine history. If steam_api.dll is there, it should be restored and the game folder should be added to the antivirus exception list.
that use the Steamworks API for features like achievements, user authentication, and DRM protection . If this file is missing, the game will fail to launch, usually displaying a "System Error" or "Unable to Initialize Steam API" message . Why is the file missing? steam api dll pes 2016 link