Plots - several pages per pdf - quality/size issue

Dear R-experts,

I hope that question will not be too redundant (sorry if it is) but i 
don't seem able to find the answer i need in the archives...

I try to create a file which would have 1.several pages and 2.several 
plots by page. I know how to make a pdf file this way, but my problem is 
that the pdf size gets way too big and cannot be open.

So my question is:
- is there a way to diminish the pdf size/quality?
- does any other file format exists that would be of smaller quality but 
still be able to print plots on several pages for the same file?

Thank you for your help!

Sarah