Alright, so when I go to Export>Save as PDF and compression set to none, the PDF file is 2.3 gigs. But when I set compression to automatic and quality to maximum, it comes out to 300 megs. All images in the document are 300 dpi and I set the maximum dpi to 300 so those hopefully didn't change.
So my question is, how can compression make such a huge difference in file size? Surely this will affect how the images look in print, or will it? Will there be a difference to the naked eye on the printed page? I would leave the compression at none, but the file size limit for the print-on-demand is 800 megs so I guess I have to do some compression during pdf export.