Unwanted white border on all PDF exports.

Hiya -

I tend to export PDFs for print a lot and I'm currently having a problem where all PDFs I export have this really annoying white border I can't get rid of. I've tried tinkering with the various design apps and bits of software that I use, initially thinking it was a problem with one of them, but now I've realise it's just Apple / my MacBook, because even exporting a random scan image as PDF from preview creates the same result.

It's destroying my mode of work and so far I've found no workarounds, so any advice would be appreciated. I can't have ugly white borders on full bleed images for the rest of time.