Simply replacing an existing file with a new version of that
file. ( No matter how many times you repeat the operation,)
does not remove the original files information from the hard
drive.
 
The file allocation table for the hard drive just marks the original
clusters of the file as junk or unused and that portion of the hard
drive may or may not ever be written to again.
 
The new version(s) of the file are created in new locations on the
harddrive.
 
You would also have to use some fairly complex APIs to do
absolute disk writes.