This post of Michael Sync will give you some tips and tricks of using Rich Textbox in WPF.
As we all know, the build-in WPF RichTexbox doesn’t provide some features that we are looking for so if you are in need of using RichTexbox in WPF project, you should know that you will need to roll your own implementation (at least) a bit. In this post, I will brief you how to make WPF RichTextbox bindable, how to display the HTML in WPF, how to create a Rich Textbox Editor with toolbar.