This CodeProject article simulates MDI in WPF:
Multiple Window Interface for WPF[
^].
Do not use MDI! This is the worse UI style, highly discourages practically be everyone. This is one of the most inconvenient designs all UI ever invented. You will only scare off your customers. Use design based on a single main window: tabbing interface, for example. (See
Tabbed MDI in WPF[
^].)
—SA