Characters evident in document (7,6)
I believe the answer is:
letters patent
'document' is the definition.
(I know that letters patent is a type of instrument)
'characters evident' is the wordplay.
'characters' becomes 'letters' (letter is a kind of character).
'evident' becomes 'patent' (synonyms).
'letters'+'patent'='LETTERS-PATENT'
'in' is the link.
(Other definitions for letters patent that I've seen before include "Legal document" , "They've given one the right" , "Official document of inventor's rights" , "Official document that confers a right" , "Document conferring a privilege" .)