Nifty macOS Catalina feature

"Click the Markup button in MacOS and there's a new button that will send images and documents over to your iPhone or iPad so you can mark it up with your fingers or an Apple Pencil (and changes are reflected in real time on the Mac's screen)."

https://arstechnica.com/gadgets/2019/10/macos-10-15-catalina-the-ars-technica-review/4/#h1