A poor book forger will risk everything (2,3,5)
I believe the answer is:
go for broke
'risk everything' is the definition.
(I've seen this in another clue)
'a poor book forger' is the wordplay.
'a poor' indicates anagramming the letters.
'book'+'forger'='bookforger'
'bookforger' is an anagram of 'GO FOR BROKE'.
'will' acts as a link.
(Other definitions for go for broke that I've seen before include "Risk everything in an all-out effort" , "Make an all-out effort" , "Make all-or-nothing effort" , "Gamble everything" .)