An MDE file is in a "compiled" state: all of the VBA code has been
compiled, the compiled version hidden, and the sourcecode removed. You
can't make any design changes to Forms or Reports.
Many developers will convert their MDB file to MDE for distribution to
users, so they can't mess with the design or read the code. It's
ESSENTIAL!! to keep a copy of the MDB file, because if you don't,
there's no way to maintain the design of the database; it's a one-way
door, you cannot convert a .mde file back to .mdb.