Not a single document, even (7)
I believe the answer is:
uniform
'even' is the definition.
(I've seen this before)
'not a single document' is the wordplay.
'not' becomes 'un' (prefix meaning 'not').
'a single' becomes 'I' (one).
'document' becomes 'form' (form is a kind of document).
'un'+'i'+'form'='UNIFORM'
(Other definitions for uniform that I've seen before include "Regimentals" , "Even; clothing" , "Codeword following Tango" , "Constant; outfit" , "Official dress" .)