If you’ve ever looked for a macOS tool that can compress PDFs, you’ve probably come across a list of dozens of apps in the Mac App Store for exactly that purpose. The problem: Most of them seem to be really old, incomplete, buggy or hardly working anymore.
One tool I can recommend (I bought it, use it almost daily and like it): PDF Squeezer (5.99 USD) (Home page)
Unlike the barely usable PDF compression feature in Apple’s Preview app (in the macOS file previewer, choose “Export…”, then “Quartz Filter: Reduce File Size”), PDF Squeezer manages to reduce a PDF file’s size by about 60-90% while retaining the original file’s legibility and good quality.
P.S. Another useful (free) tool from the same publisher, the PDF Print Service Creator, can be downloaded for free and allows to customize macOS’s print dialog in order to send any printable document directly to any of the apps that are capable of opening PDFs.