The initial post is old, but try this :
HttpContext.Current.Response.ClearContent();
HttpContext.Current.Response.ClearHeaders();
HttpContext.Current.Response.ContentType = "application/pdf";
HttpContext.Current.Response.AppendHeader("content-disposition", "attachment; filename=" + fileName);
System.IO.MemoryStream stmMemory = new System.IO.MemoryStream();
CuteEditor.Convertor.PDF.
HTML2PDF convertor = new CuteEditor.Convertor.PDF.HTML2PDF(Server.HtmlDecode(this.RTE.XHTML));
convertor.RenderSinglePageContent =
false;
convertor.Render();
convertor.Save(stmMemory);
stmMemory.WriteTo(
HttpContext.Current.Response.OutputStream);
stmMemory.Close();
stmMemory.Dispose();
Response.End();