I have a PDF file that is 600 + MB in size. I opened it in Preview, selected "Export" from the File menu. In the window that opened, I chose "PDF" as Format, and from the Quartz Filter menu I chose "Reduce file size 75%," (an option I think may have added using the Color Sync Utility several years ago). The resulting exported file was actually larger in file size than the original PDF document. I've tried "Export to PDF," and I've been trying to export it from "Print" as well. Although there is some variation, all exported PDFs are larger than 600 MB.