I have tried to reproduce the unexpected behavior but to no avail - the PDF document is properly opening in the RadWindow as well as in the iframe element in FireFox and Internet Explorer. Could you please have a look at the attached video and then tell me what I am missing?
What I can suggest you is try to open the PDF document in a simple Iframe element. If the document is not opened there, then it will not be opened in the RadWindow neither, as it uses an iframe, so that would be a browser behavior that we do not have control over it.
Otherwise I can suggest that you reproduce the issue with the attached VS example and then provide us with the modification, so that we can make an investigation on our side.
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