Here's a standard English sentence:
The folder which is missing from the principal's office contained the answers to today's exam.
(Separate question, discussed elsewhere I'm sure, whether it should really be "which" or "that".)
But simpler is usually better, so I would actually just write:
The folder missing from the principal's office ...
But my question is: I have seen legal statements which would write:
The folder, which folder is missing from the principal's office, contained ...
Assuming that the writer is actually correct in thinking that s/he's adding some value by repeating "folder" after the "which", what value is s/he adding?