Well, one thing I had to think about some days ago: If no one can crack a cod-file, everybody can also easily find and delete them. Other wordprocessors are using for saving a codified document the same extension as for other documents, hiding the really sensible stuff among the mass of letters and reports.
I am not sure that changing the file extension of the encrypted document would help to "hide" it. But you can change the file extension of your COD file to "rtf" or "doc". Atlantis would still know that this document is encrypted.
