Private documents one sent up to Charlie (5)
I believe the answer is:
idiot
'charlie' is the definition.
(I've seen this before)
'private documents one sent up to' is the wordplay.
'private documents' becomes 'ID' (as in identification papers).
'one' becomes 'i' (Roman numeral).
'sent up' says the letters should be written backwards.
'to' written backwards gives 'ot'.
'id'+'i'+'ot'='IDIOT'
(Other definitions for idiot that I've seen before include "Jackass" , "Clot" , "Goose" , "Ass, nincompoop" , "Simpleton" .)