I tested your code but the PDF document is correctly loaded in IE on my side - please examine the attached iframe_contenttemplate_IE.jpg screenshot. What i can assume is that for some reason the path to the file is incorrect or your browser has some plugin installed which prevents the loading of the PDF.
On a side note, you can load a PDF document in RadWindow without putting an IFRAME there, by directly setting the NavigateUrl to th epath as follows:
In this manner the RadWindow will not only automatically create an IFRAME inside itself but it will also resize it when the RadWindow is resized, you can use the OnClientPageLoad client event, etc. and that is why i suggest to examine this configuration too and take advantage of built-in features if they fit your requirements.
To test whether the issue is in path or browser plugin, I suggest you test with my test demo I attached to the thread /I put 2 RadWindows with both the ContentTemplate and the NavigateUrl approaches for your reference/ and test under IE on your side.
I hope that my reply and suggestions are detailed enough and helpful, let me know how it goes.
All the best,
the Telerik team
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