RadWindow is just a container and does not offer the requested functionality. Its content area is a standard DIV (ContentTemplate) or IFRAME (NavigeUrl)
and it is up to the developer to obtain its content and decide how to transform it using third party tools or personal code to the desired format.
You can find information how to access controls placed inside the ContentTemplate of RadWindow in the following article: Using RadWindow as controls container
If you unable to implement your scenario with RadWindow, try to implement it with a standard asp:PlaceHolder and when you are ready replace the placeholder with RadWindow.
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