Simple account in dossier (6)
I believe the answer is:
facile
'simple' is the definition.
(thesaurus)
'account in dossier' is the wordplay.
'account' becomes 'ac' (abbreviation for account).
'in' indicates putting letters inside.
'dossier' becomes 'file' (a dossier is a file or set of information).
'ac' inserted into 'file' is 'FACILE'.
(Other definitions for facile that I've seen before include "Easy or superficial" , "A piece of cake" , "Easily achieved but of little value" , "Too easily achieved, glib" , "Easy but glib" .)