Destroy section of dossier as evidence (5)
I believe the answer is:
erase
'destroy' is the definition.
(thesaurus)
'section of dossier as evidence' is the wordplay.
'section of' indicates a hidden word.
'ERASE' can be found hidden inside 'dossier as evidence'.
(Other definitions for erase that I've seen before include "Remove recorded material" , "To remove all trace" , "Take out" , "Clear" , "Remove from memory" .)