Converting one XML document into another XML document

XElement newOrder = new XElement("Order");
newOrder.Add(new XElement("OrderId", (string)oldOrder.Element("OrderId")),
newOrder.Add(new XElement("OrderName", (string)oldOrder.Element("OrderName")),
...............
...............
...............and so on

List<string> elementNames = GetElementNames();

newOrder.Add(
  elementNames
    .Select(name => GetElement(name, oldOrder))
    .Where(element => element != null)
    .ToArray()
  );

public XElement GetElement(string name, XElement source)
{
  XElement result = null;
  XElement original = source.Elements(name).FirstOrDefault();
  if (original != null)
  {
    result = new XElement(name, (string)original)
  }
  return result;
}