RadWindow merely passes the URL the developer provides to a simple iframe to load the designated document. It does not change it and it does not control the content the server sends.
Most likely, the page you open has a master page with the menus and the other elements you do not want. In this case you would need to consider removing/hiding them according to an additional querystring param, or using a different master page, if possible.
Once you can put the same URL in a simple iframe and show the desired content, the RadWindow should behave in the same way.
On a side note - to set the RadWindow title you should use the RadWindow instance and its set_title() method instead of a method on the RadWindowManager. The manager's open() method returns the RadWindow instance for you to use.
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