Hi Abhishek Gairola,
RadRichTextBox was introduced in Q2 2010, so you will not have it in your version of the controls. However, it has evolved pretty much since then and it would be best if you upgrade to the latest version of the controls, which is 2010 Q3 Service Pack 1 (2010.3.1314).
If you have any other questions, do not hesitate to contact us again.
the Telerik team
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