You cannot save files on the client in any other way than the SaveFileDialog due to Silverlight's security policy. If you want to save the file on the server, you can either export the content of the document to a stream in the Silverlight application and use a WebClient to pass the stream to the server or use the WPF assemblies in the ASP project and export the document there. There is a demo with RadRichTextBox and WCF services, which you mind find helpful, in this forum thread.
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