How to select a word at runtime in richtextbox

Question

Dear friends,

I am developing a spell checker, I want to get the data in richtextbox spell checked and that I am able to do it. But I want to highlight the word which is wrongly spelled and let it remain highlighted till replaced. I have adopted the method of richtextbox select and have provided the range also, but not able to correctly select the word at the runtime. Is there any method or logic to do so.

Thanking you in anticipation.