My experience tells me to do two things, first, scan at 300 dpi, save then "Reduce File Size" in Acrobat's File Menu and second leave those PDF's out of FileMaker they make your system sluggish. Use a plug-in that allows you to manage, move and open the files in your computer and only keep the actual address in your database.
I usually export from FM layout to pdf; such as summary, report, invoice and so on.
Usually there is no images (at least a small and optimized logo in a global container field), but only layout element, colored fileds and sections.
I expect that document like this is smaller than FileMaker normally does....
This I mean