This post summarizes some ways to compress PDF files.
Free methods to compress PDFs
Free Online Tools
I Love PDF
CIB pdf standalone
Paid methods to compress PDFs
Paid Online Tools
Paid Applications
Adobe Acrobat
Open Acrobat Reader and go to menu bar > File > “Compress file”. This option is also available on free versions, but it require that you activate the trial period of the paid version. After this period, you will need to pay to keep using premium functionality like PDF compression.