To host the WPF composite control, the ElementHost object is used inside the Windows Forms host application. The ElementHost class is part of the System.Windows.Forms.Integration namespace, and thus you will need to reference the WindowsFormsIntegration.dll in the project.
To host a WPF element in a Windows Form, you must assign it to the Child property of the ElementHost control. If it is required, use the PropertyMap property to assign the custom mappings between an ElementHost and its hosted WPF element. Optionally, you can use the boolean BackColorTransparent property to set a transparent background to the hosted element.