This file is a harmful and undesirable program. Probably virus. It's recommended to delete it.
What is sf.exe Windows startup process
File name: sf.exe
Program name: sf
Description: WIN32.FAVADD.O TROJAN
Information added by: sukuba at 08 August 2008
Hint: If sf.exe file is a virus or trojan, we recommend to use a antivirus software or registry cleaner.