Reach conclusion from reading file (5)
I believe the answer is:
grasp
'reach' is the definition.
('grasp' can be a synonym of 'reach')
'conclusion from reading file' is the wordplay.
'conclusion from' says to take the final letters.
'file' becomes 'rasp' (rasp is a kind of file).
The final letter of 'reading' is 'g'.
'g'+'rasp'='GRASP'
(Other definitions for grasp that I've seen before include "Seize firmly - or understand (5)" , "Firmly grip" , "Support; rugby player" , "Lay hold of" , "Understand (the point)" .)