Have you just tried using iCloud drive on the Mac and the "Files" app on the phone/iPad?

Apps are opened and marked in Preview on the Mac and in-app markup is allowed in Files.

All changes are synced. Elegant. Free. Baked-in using no extra apps.

Have you just tried using iCloud drive on the Mac and the "Files" app on the phone/iPad, with shelves represented by sub-folders?

Apps are opened and marked in Preview on the Mac and in-app markup is allowed in Files.

All changes are synced. Elegant. Free. Baked-in using no extra apps.