I am currently in the middle of creating a new book of my work. This involves going through a lot of images, figuring out what works, designing a layout, and a host of other things.

Today I wanted to email a current version of the book in PDF format to a friend. While I created the book in Aperture, the file was too large to email (over 100 MB). I found no function in Aperture to control the image quality. I also tried resaving it using the Preview app, but found no options there either.
After digging around online, I found this great (and completely hidden) tip: use the ColorSync Utility app. Open this app (located in /Applications/Utilities). Then, use the File menu to open your ginormous PDF file. Once open, at the bottom of the window you’ll see a Filter menu. In there is an option to Reduce File Size.

Why on earth this is in the ColorSync Utility and not in Preview, I’ll never know. And doubly-so as to why reducing file size would be called a ‘filter’. In any case, it worked like a charm, shrinking my 100MB+ file down to a much-more-manageable 700k!