Something fantastic has happened and I need to bring it to your attention.
I get so annoyed trying to read pdfs that have lots of space around the text.
Maybe you feel the same.
Zooming in and out every page is such a faff.
Well, it turns out you can crop pdfs really easily using the mac pdf viewer!
Just select the appropriate rectangle (tools>>rectangular selection),
then enable thumbnail view (view>>thumbnails),
select all (cmnd-a) and finally
press cmnd-k.
I'm so happy right now.