Pages v5.5.2 will allow you to drag/drop files, or folders in the open dialog into other locations using the sidebar Favorites as targets, but not other folders in the current open dialog view. Without an option key modifier, these drag/drop operations are move, not copy activity.
One cannot drag/drop a file object from the Desktop into the open dialog positioned in ~/Documents, as the dropping action is ignored, and switches the open dialog view to the Desktop.
If you have an existing Pages document open, and with Save As… you decide to drag/drop a folder from the Save dialog's Desktop view into the Favorites Document location, the Save dialog will close, without saving the current document, or moving the folder from the Desktop. The same activity with iCloud Drive as a destination will move the Desktop folder into iCloud Drive, and keep the Save As dialog open. Still in the Pages Save As dialog, you can click on iCloud Drive, and then drag/drop that folder back to the Desktop, with the Save As dialog remaining open.
I just did more testing than Apple has done in the entire application.