If you own the game, do not download a DLL from a website; force Steam to give you the correct one. If you are dealing with a modified version, you must whitelist the file in your antivirus, as Windows will relentlessly attempt to delete it.
(These are the DLC app IDs for the Professional Edition bonuses.) steamapidll for hitman absolution professional edition best
: Managing the Steam Overlay and syncing game data with Steam servers. If you own the game, do not download
For the Professional Edition , the stakes are higher: replacing steamapi.dll can cause the game to fail recognizing the Professional Edition extras, leading to missing weapons, suits, or the Sniper Challenge launcher. If you own the game