From what program are you making the PDF? In photoshop you have some command over PDF quality. The default printing setting for PDF's is set to 600dpi [via Cute PDF et al]. You can lower this in custom settings. It depends on how many images, how many pages... How big is big? What is the original DPI of the images, etc, etc.

i created the pdf in illustrator with images from photoshop. one page size is for eg 18mb so i basically would like to make a smaller file without going back into photoshop to reduce the image resolutions etc
thanks

Are you saving as a PDF or prting it as a PDF?

I got Illustrator CS2, and you can choose a preset quality of PDF when you save, eg, Adobe PDF Medium, High Quality print, Smallest File Size. You can then experiment and alter the existing presets.

i am saving as a pdf and using illustrator 9 i'm not sure if it has those settings for saving do you?
thanks

Should do. You get a dialog box when you save as a PDF.

ok thanks

i'm using illustrator 9 and would like to make smaller pdf file sizes using the settings that gives me the options for medium, high quality file etc . does anyone know if illustrator9 has that option. i can't seem to find it in either the save as or print dialog boxes. any help
thanks

if what you're trying doesn't work, maybe just export as a raster graphic in .tif format. I've got a habit of having huge AI files, with hi-res images, and simply export to raster graphic at whatever size i need to print/project at 300 DPI. then just open Pshop or acrobat and make that a pdf.

yeah it's a backwards process.

On the pdf settings there should be a checked box labled "Preserve Illustrator Editing Capabilities". Uncheck the box, and your file size usually will go down to 1/4 what it used to be. This preserves the same visual quality, but destroys the layering, so it's the best thing to use if you're sending someone (like a printer or potential employer) a file to view, but not edit.

To follow up on rationalist's great suggestion, if you're in pshop, flatten the file, then save as PDF. It should be a lot smaller without all of the layer information.

thanks guys