Encode["source", "dest"] writes an encoded version of the file source to the file dest.
<<dest decodes the file before reading its contents.
Encode["source", "dest", "key"] produces an encoded file which must be read in using Get["dest", "key"].
Encoded files contain only printable ASCII characters. They begin with a special sequence which is recognized by Get.
On certain computer systems Encode["source", "dest", MachineID->"ID"] can be used to generate an encoded file which can be read in only on a computer with a particular $MachineID.
No function is provided in Mathematica to convert encoded files back to their original form.
See The Mathematica Book: Section 2.11.1.
See also: ReadProtected, $MachineID.