Net profit at last drawn that voids margins (5)
I believe the answer is:
tulle
'net profit' is the definition.
'tulle' can be an answer for 'net' (net used in dressmaking). I am not sure about the 'profit' bit.
'last drawn that voids margins' is the wordplay.
'last' becomes 't' (I've seen this in other clues).
'drawn' becomes 'pulled' (pulling is a kind of drawing).
'that voids margins' means to look at the middle letters (the letters on the margins of the word are removed).
The centre of 'pulled' is 'ulle'.
't'+'ulle'='TULLE'
'at' acts as a link.
(Other definitions for tulle that I've seen before include "Fine netting used for veils" , "Veil material" , "Silk net fabric" , "Delicate netted fabric" , "Fine net material" .)