You can sign a PDF on your Mac using the giant MacBook trackpad, and you can mark up PDFs and screenshots, too. But all that stuff is much easier on the iPad, especially if you have an Apple Pencil. The problem is getting it there. But in macOS Catalina, you don’t have to “get it” anywhere. Screenshots and PDFs magically show up on nearby iPads, where you can sign them or mark them up. Then you can return them to your Mac. These features are called Continuity Sketch and Continuity Markup, and they’re killer.
You know how the UPS guy holds up his brown scanner box for you to sign? PDF markup is like that, only on your iPad — and you never feel guilty about ordering too many parcels.