From memory, you need to go into the Accessories settings of the Control Panel, from there, head to 'Ease of Access', then you can click the 'On-Screen Keyboard'.
I seem to recall that its more of a Windows setting than a PAC Display setting.
(At the password prompt, its a system call, not a pac display call).
All that said, make sure that in PAC Display Configurator, under the menu 'Configure -> Runtime', you have both options ticked;
'Use on-screen keyboard for touchscreens' and
'Include 'Insert ASCII' in screen-keyboard'.