Customs document chap provided is in French (8)
I believe the answer is:
manifest
'customs document' is the definition.
(I've seen this in another clue)
'chap provided is in french' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'provided' becomes 'if' (eg 'provided it's sunny' means 'if it's sunny').
'is in french' becomes 'est' ('is' in French).
'man'+'if'+'est'='MANIFEST'
(Other definitions for manifest that I've seen before include "Obvious, cargo listing" , "Evident" , "Display" , "Become apparent" , "list of passengers flying" .)