Doctor behind preliminary version (5)
I believe the answer is:
draft
'preliminary version' is the definition.
(I've seen this in another clue)
'doctor behind' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'behind' becomes 'aft' (aft means towards or at the end of a ship).
'dr'+'aft'='DRAFT'
(Other definitions for draft that I've seen before include "Rough version" , "Current of air or preliminary sketch" , "Preliminary text or plan" , "A money order for US conscription" , "Outline or sketch" .)