Print file using Adobe Print driver
The easiest way to try and shrink a PDF file is to perform a little trick, which basically is printing the PDF document to a PDF file. Sounds strange? It is. Basically, you open the PDF file in Adobe Reader and print it to the Adobe PDF printer.
Amazingly enough, I’ve been able to shrink a 20 MB PDF file down to 3 MB just by using this method. Not really sure what it does to shrink it, but it works, especially if you have a good number of images that are eating up a lot of space.