Shrink PDF Files in OS X and Control Image Quality

This guide is using information from here and providing clearer instructions and a Automator script to compress many at once.

• Go here and click the green Clone or download button, then select Download ZIP.
• Go to Downloads on your computer and rename the downloaded folder to Filters.
• Make a new Finder window (Command+n) and then hold Option while clicking Go -> Library in the menu.
• Drag the Filters folder with he files you downloaded into this new Library folder.
• Download this program to your Applications folder or Desktop.
• Now you can just all your PDF's files at once and drop them onto the application and it will compress them and save the compressed versions to your desktop.