Different from document (4)
I believe the answer is:
form
'document' is the definition.
(I've seen this before)
'different from' is the wordplay.
'different' is an anagram indicator.
'from' anagrammed gives 'FORM'.
(Other definitions for form that I've seen before include "Seat" , "Hare's home - something to be filled in" , "'Shape, bench or school class (4)'" , "Criminal record (colloq.)" , "Class in a school, or the shape of something" .)