im searching for a Usercontrol that generates XAML-Code (Flowdocument Code)
For a Bold Text -> <Paragraph><Bold>Text</Bold></Paragraph>
You may want to have a look at the RichTextBox in the Extended WPF Toolkit - http://wpftoolkit.codeplex.com/wikipage?title=RichTextBox
I haven't tried it, but according to the documentation it has a XamlFormatter as well.