I tryed below with no success in preserving CDATA.
How it can be done?

public static void XmlInclude(string inputUri, string outputUri)
{
   using (XIncludingReader xir = new XIncludingReader(inputUri))
   {
      xir.ExposeTextInclusionsAsCDATA = true;
      if (xir.Read())
      {
         string s = xir.ReadOuterXml();
         File.WriteAllText(outputUri, s);
      }
   }
}