>Has anybody tried it? And if it's not advisable, what's the alternative organization for a transaction based (desktop) application that requires a large amount of different forms? Tabcontrol will only allow a limited amount of different forms, and the forms cannot be viewed simultaneously.
>
>And if I do insist on mdi, I'd better go WinForm than WPF?

Googling 'WPF MDI' birings up a few libraries that supposedly implement a MDI interface. Haven't tried them but

http://wpfmdi.codeplex.com/ looks interesting.
http://avalondock.codeplex.com/ isn't really an MDI but could be a good design alternative.

But MDI is going out of fashion - users can easily be confused. You can have a lot of forms opened simultaneously - but how many can be actually visible at any one time.

WPF has the ability to provide a VS type interface with vertical, horizontal and floating tab groups. There are a few 3rd party libraries to simplify this.

Also have a look at Prism : https://msdn.microsoft.com/en-us/library/ff648465.aspx
A nice way of controlling multiple views.....