[DLL-Files Support 2016-06-01]steam_apir.dll
The steam_apir.dll seems to only be used for breaking copyright protection on games. It is also identified as a threat by multiple antivirus
This file being missing is likely caused by your antivirus removing it after identifying it as a threat.
If you trust this file, re-install the program requesting it, and make sure your antivirus does not interfer.
Some scan results of this file;