Optimize a PDF on Mac

Preview ships with a Quartz filter called Reduce File Size, and it is the first thing most Mac users try. The trouble is that it applies one fixed, fairly aggressive image downsampling recipe to the whole document regardless of what is in it. On a text heavy PDF it does almost nothing, and on an image heavy one it can crush photos to a blocky, washed out mess. Because the recipe is not adjustable without editing filter files by hand, you get whatever Apple chose years ago, take it or leave it.

FixTools approaches the file differently. Instead of downsampling images by default, it performs lossless structural optimization, removing the parts of the file that add size without adding anything visible. For the very common case of a Pages or Keynote export, a print to PDF, or a document that was edited and re-saved several times, that hidden overhead is often where the excess size lives, and clearing it out shrinks the file without any of the image damage the Quartz filter can cause.

When your Mac PDF is large specifically because of high resolution photographs or scanned pages, and you genuinely need it much smaller, the honest answer is that you do want image compression, just done well. In that case use the PDF Compressor, which lets the reduction go far beyond what structural optimization can reach, with a controlled quality tradeoff that is usually invisible on a Retina display at normal zoom.