Just completed dragging / dropping a file from my MBP's Desktop to my iCloud Drive in the Sidebar. ...Result was file no longer on my Desktop, but in my iCloud Drive. So, the file was
moved to my iCloud Drive and an internet connection (of some means) now required to view / edit the doc(s) in my iCloud Drive from any of my devices.
I checked my iPhone's Files app (showing what's in iCloud Drive) and the doc (a pdf) was in the subfolder of my iCD where I'd dragged / dropped it.
Here's a link to
iCloud Drive FAQ Here's a link to
iCloud Drive Security 
