Test 1
Opened a Finder window, chose AirDrop in the sidebar, then dragged and dropped a .PDF file to the icon in the AirDrop window that represented the iPhone. The .PDF file showed up in the Downloads folder on iCloud Drive.
Test 2
Imported .PDF file into the Books application on the Macintosh. I didn't see any way to AirDrop something from Books to anywhere else, so I ran the Books app on the iPhone. The .PDF showed up as part of the Library with a "cloud" icon to show that it was available, but had not yet been downloaded from iCloud.
When I look in iCloud settings, Books does not show up in the iCloud settings for the Mac. It does show up in the settings for the iPhone, and there, the switch is turned on.
Note: Both tests conducted with a Mac running Ventura and an iPhone running iOS 17.