How does my handwriting turn into a PDF I can read on my Mac?

Your Supernote stores pages in its own ".note" format, which a normal PDF reader can't open. When you open a linked note, the app quietly pulls that raw .note file off your device over Wi-Fi and runs it through a built-in converter that re-draws every page faithfully (ink, shapes and all) into a standard PDF. The conversion happens on your own Mac — nothing is sent to the cloud.