Currently, the mail merge feature is not supported by RadRichTextBox for WinForms
. I logged this as a feature request in our issue tracking system. However, currently this feature is not scheduled in our plans and I cannot give you a time frame in which it will be implemented. We may raise the priority of this feature when more people request the same. I updated your Telerik points for suggesting this feature.
Should you have any other questions, do not hesitate to ask.
the Telerik team