In your code sample you should change the document to contentDocument since the latter is the correct property of an iframe:
iframe = $find(
"<%= ContentPane.ClientID %>"
document.title = iframe.contentDocument.title;
Please, note that if the content of the iframe is from another domain, the above code will violate the cross-domain constraints and it is very likely to fail.
Another options is to try setting the title of the hosting window from the loaded content using the top
reference. Therefore in the content page you could do something like this:
top.document.title = document.title;
Hope this helps.
All the best,
the Telerik team
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