Document to fill out (4)
I believe the answer is:
form
'document to fill out' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for form that I've seen before include "Home of a hare" , "Configuration; type" , "A class in a school or a hare's lair" , "accommodation for hare" , "Class - questionnaire" .)