How to render rdlc report to .docx not as doc

var report = new LocalReport();
RvQpTemplate.LocalReport.DataSources.Add(new Microsoft.Reporting.WebForms.ReportDataSource());
RvQpTemplate.DataBind();

Byte[] mybytes = RvQpTemplate.LocalReport.Render("WORD", null,
                out extension, out encoding,
                out mimeType, out streams, out warnings);
Response.ClearHeaders();
Response.ClearContent();
Response.Buffer = true;
Response.Clear();
Response.ContentType = contentType;
Response.AddHeader("Content-Disposition", "attachment; filename="+test.docx);
Response.BinaryWrite(mybytes);
Response.Flush();
Response.Close();
Response.End();