When I worked in the Linux world I used a variety of command line tools to help reduce the size of large PDF files. In the Mac OSX world I started looking at converting some of my same scripts over to run on OS X. There were several tools I needed to install via MacPorts and as I started that process I realized there was probably a simpler way already built into OS X. Sure enough, there is: Automator.

To all you long time Apple users Automator is old news, but it was new to me. Here is how I created an Automator workflow (and then app) to reduce PDF large files down to size by shrinking the images inside the PDF.

Open Automator and choose to create a new application.
From the Library choose PDFs.
Drag the item labeled “Apply Quartz Filter to PDF Documents” to the workflow area.

I could choose the filter called “Reduce File Size” but I want to make some adjustments to it and the default filter is locked so click the Advanced options and from the list option-click (or two finger tap) the Reduce File Size filter and choose Duplicate.

Now spin down your copy of the filter and adjust the Image Sampling and Image Compression settings. For sampling I used 50% scale, 1024 max pixels, 128 min pixels and High quality. For compression I used JPEG mode and set the quality a few notches below Max.

Now in the filter dropdown at the top choose your Reduce File Size Copy filter.

I want the PDF to be opened after reduction so go to your library and choose Files and Folders and drag over the Open Finder Items action.

Make sure Open with is set to “Default Application”.

Now save your workflow and put your compiled app on your desktop or somewhere handy. Any time you need to reduce a PDF drop it on the app icon and your PDF will be reduced and opened in Preview.