I am pasting here the answer we have provided in your ticket with the same question:
There is no feature or utility in RadEditor that can help you out with such a requirement.
Such a functionality/feature can be achieved only as a custom solution, by using the DOM events of the HTML document. Here it is shown how you can attach DOM events to the content area—http://docs.telerik.com/devtools/aspnet-ajax/controls/editor/client-side-programming/events/onclientload.
Using the DOM events you can capture the which key is pressed and programmatically interfere with the content.
On a site note - I deleted your other forum threads with the same question as they only create duplicates and make information harder to track.
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