"Determine file types by examining file contents" scans a specific, configurable group of file extensions that contain executable code, and all .exe and .doc files. It also reads each file's header to determine its file type. It scans .exe and .doc files even if a virus changes their file extensions."
Essentially the feature enables scanning of .exe executables and Office documents regardless of extension in addition to scanning files based on selected extensions, scans all executables and documents based on file contents.