If you are using a cracked version (e.g., RELOADED, CPY, or 3DM), the crack includes a specific steam-api.dll that emulates Steam. Reinstalling the crack will restore it.
flagged it as a "false positive" and quarantined or deleted it. This often happens with game cracks or patches used in older titles. How to Fix the Error Check Your Antivirus Quarantine download steam-api.dll for pes 2016