This guide is applicable to Windows 8 and Windows 10 tablets. It is very annoying that the virtual on-screen keyboard kept on popping up even when the Bluetooth keyboard was connected.
To disable the on screen keyboard, at the Windows->Search bar, just type “Typing settings” and click it which will lead you to the screenshot below. Just turn OFF the last selection “Show the touch keyboard or handwriting panel when not in tablet mode and there’s no keyboard attached”
For hiding keyboard in Android tablets, please refer here.