function ExpandFileName(const FileName: String): String;
Returns a string containing a fully qualified path name for the file passed in FileName. A fully qualified path name includes the drive letter and any directory and subdirectories in addition to the file name and extension.
An empty string is returned if the input is an empty string or contains only spaces.
An exception will be raised upon failure, which is only known to happen when the input or output path exceeds 32K characters.