Shape of an official document (4)
I believe the answer is:
form
I believe this clue is a double definition.
'shape' is the first definition.
(I know that shape can be written as form)
'an official document' is the second definition.
(thesaurus)
'of' is the link.
(Other definitions for form that I've seen before include "'Shape, bench or school class (4)'" , "Make" , "Criminal record (colloq.)" , "Group of schoolchildren < > construct" , "A class in a school or a hare's lair" .)