The most proper and supported solutions for MVC is using the controls from the UI for ASP.NET MVC
suite. In this case RadEditor UI for ASP.NET MVC
The controls from the UI for ASP.NET AJAX suite are not support under MVC environments—http://docs.telerik.com/devtools/aspnet-ajax/mvc/overview
. The main reason for that is the lack of page life cycle, which exists only in WebForms applications.
You can alternatively use mixture of MVC and WebForms, where you can create aspx pages inside MVC environment. You can find plenty of information about that in public discussions and resources through the internet (e.g., http://stackoverflow.com/questions/25385532/how-to-add-aspx-pages-to-existing-mvc-4-project
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