Private documents one returned to Charlie (5)
I believe the answer is:
idiot
'charlie' is the definition.
(I've seen this before)
'private documents one returned to' is the wordplay.
'private documents' becomes 'id' (as in identification papers).
'one' becomes 'i' (Roman numeral).
'returned' says the letters should be written in reverse.
'to' backwards is 'ot'.
'id'+'i'+'ot'='IDIOT'
(Other definitions for idiot that I've seen before include "Ass, nincompoop" , "Blockhead" , "Twit" , "Ignoramus's" , "nutter" .)