Cheat by hiding some files between book-ends (4)
I believe the answer is:
bilk
'cheat' is the definition.
(I know that bilk is a more specific form of the action cheat)
'by hiding some files between book-ends' is the wordplay.
'by hiding' becomes 'i' (I can't explain this - if you can you should give a lot more credence to this answer).
'some' says to take the centre.
'between' means one lot of letters goes inside another.
'ends' means to remove the middle letters.
The centre of 'files' is 'l'.
'book' with its centre taken out is 'bk'.
'i'+'l'='il'
'il' going within 'bk' is 'BILK'.
Can you help me to learn more?
(Other definitions for bilk that I've seen before include "fleece" , "Acker --, jazzman" , "Defraud; Acker --, clarinettist" , "Thwart" , "Cheat (of payment)" .)