- you have to open schematic editor as I have written. Under Windows it is the eeschema.exe file in the KiCad\bin directory.
- open in that program (looks a little different than schematic editor opened from KiCad main application window) the source schematic.
- select the part of schematic with mouse and then right-click and ‘Copy Block’ (there is Ctrl+C written there so I suppose it also works).
- open the destination schematic (in the same program, when I tried to open in second schematic editor instance it didn’t worked).
- right-click and ‘Paste’ (probably Ctrl+V also works).
I am using 5.1.6.