I have a rich text document which I have gone through and put "<<" and ">>" around keywords that I want to have a Mail Merge fields. I have tired to put in the merge fields in the XAML, but does not work well. What is the best way to programatically search through the text of a RadDocument and replace some text with MailMerge fields.

Hi Clifford,
For searching/replacing content in the document, you can use DocumentTextSearch class and its FindAll method, as described in this help article. Note that the parameter of FindAll method is a regex. After fingind the necessary text ranges, you can replace them using RadDocumentEditor's (or RadRichTextBox's) method InsertField with appropriate MergeField as argument, as described here.

Regards,
Boby
Telerik