CopyFile["", ""] copies to .
must already exist; must not.
CopyFile sets the modification date for to be the same as for .
CopyFile returns the full name of the file it copies to, and $Failed if it cannot do the copy.
See The Mathematica Book: Section 1.11.2 and Section 2.11.6.
See also: RenameFile, DeleteFile, CopyDirectory.