Type “gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=setting -sOutputFile=output.pdf input.pdf” into the Terminal window, replacing “input.pdf” with the name of your PDF file and “setting” with a desired quality level, and then press “Enter.”
Quality level settings are “/screen,” the lowest resolution and lowest file size, but fine for viewing on a screen; “/ebook,” a mid-point in resolution and file size; “/printer” and “/prepress,” high-quality settings used for printing PDFs.

disable relaying

In normal configuration, Syncthing will always connect to relays, as it cannot know, if other devices need them and will connect through them to it.
To be totally private (to the extreme), disable relay and global/local discovery, set the listening address to something explicit, like tcp://:22000 instead of default and set the addresses of the remote devices to their hostname/ip address and port (like tcp:// instead of dynamic. And disable usage reporting and auto upgrade (if you really want).
Then the only connections Syncthing will ever make are direct connections to the other syncthing devices.