Information: error message when you call the window.open method from a Web page to open an active document in Internet Explorer: "permission denied"
When Internet Explorer uses an Active Document server, such as Microsoft Word, Microsoft Excel, or Adobe Reader, to display a document in an Internet Explorer window, the page contains only the active document window and not the MSHTML. Therefore, the window object that is returned by the window.open method is disconnected and is invalidated. Only the IWebBrowser2 browser frame and the active document remain in the new window. Because the methods of the IWebBrowser2 interface are not exposed to scripts, you cannot call the methods of the browser frame by using a script.
Source: http://support.microsoft.com/default.aspx/kb/934365