I need to compress a PDF to 5 mb (at most, but best exactly)
Download those filters:
https://github.com/joshcarr/Apple-Quartz-Filters/archive/master.zip
Copy them in your mac or user Library ( /Library or /Users/YOURUSERNAME/Library) In a Folder named "Filters" (create if doesn't exist).
Open Preview and export as a PDF.
Try some of new filter since when you reach the right weight for your pdf.