On the Mac, printing a document to a PDF sometimes results in a very big file, for example when the original document has lots and lots of pictures in it. To make a smaller PDF :-
1. Save to PDF in the normal way.
2. Open the big PDF file using Preview (the default Apple PDF viewing application).
3. Pick: File / Save As
4. Set: Format = PDF
5. Set: Quartz Filter = Reduce File Size
I've just reduced a 12-page file from 15 MB to 1 MB by this method.