Often (and especially when scanning documents with my printer) from MacOSX I would get unreasonable huge PDFs which are not suitable for emails.
To strip them down without pain one can use ghostprint:
gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -sOutputFile=output.pdf input.pdf
gs installed, one can just brew it:
brew install gs