You can crop it beforehand (using briss for example). But if you're willing to jailbreak the kindle (which is pretty easy), I'll recommend you an alternative pdf viewer (
https://www.mobileread.com/forums/sho...d.php?t=157047) which can crop the white margin and set custom zooms, and even read multi column pdf. Also, you can try duokan, which is an alternative OS for the kindle