You can use GhostScript for reducing the size of a pdf
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dBATCH -dQUIET -sOutputFile=hector_nuba_.pdf hector_nuba.pdf
There are several options:
-dPDFSETTINGS=/screen (75ppp) -dPDFSETTINGS=/ebook (150ppp) -dPDFSETTINGS=/printer (300ppp)
If you use the printer option you may get a message about the colorspace, you can use this option:
-dUseCIEColor
I saw this iI saw this in http://milan.kupcevic.net/ghostscript-ps-pdf/