OK, the closing the window was only an example. As far the Form, ShowPopUp() could the way, how to close it and it seems to be useful trick. Thanks. I will consider it in my next design.
But actually, the capturing tool I need for my user DateTimePicker controller (the currently supported in the VWGui I dont like because of some properties which I cannot modify), which has a textbox, click-able picture / button, that opens a calendar by expanding the controller (User DateTimePicker) borders by calendar height after user mouse click at the button (picture). The controller borders are collapsed by callendar height after again user click at the button (hiding the calendar). The calendar is positioned below to the textbox and the button.
Everything is fine expect that that collapsing (hiding) the calendar must be evoked by mouse clicking outside the controller. But the controller is not a window. This is my main problem :)