Life-changing folder (4)
I believe the answer is:
file
'folder' is the definition.
(file folder is a kind of folder)
'life-changing' is the wordplay.
'changing' indicates anagramming the letters.
'life' anagrammed gives 'FILE'.
(Other definitions for file that I've seen before include "Line of people, one behind the other" , "Dossier; line of people" , "Smoothing tool; organised data" , "Set of related records kept together" , "(Set of) documents- line" .)