RadEditor is an XHTML editor, so it cannot display a PDF. It can take a simple string (which can contain HTML markup) for its Content, but it cannot take an array representation of a file. Also, if you need buttons that invoke server actions, they should be outside of the editor so they can POST the form.
What I can suggest is opening your PDF file in the RadPdfViewer for Silverlight: http://www.telerik.com/help/silverlight/radpdfviewer-overview.html. You can also consider other viewer options like the PDF.js library from Firefox and this blog can help you get started with it: http://blogs.telerik.com/aspnet-ajax/posts/14-05-27/building-an-asp.net-pdf-viewer-with-telerik-window-control-and-pdf-js.
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