DataSet ds = new DataSet();
ds.ReadXml(XMLFile);

using (XmlReader xmlreader = XmlReader.Create(ktdXMLFile.FullName))
                    {
                        xmlreader.Read(); 
                        xmlreader.ReadStartElement("KTDout", "KTDout");
                        xmlreader.ReadStartElement("GtdRegistryNumber", "KTDout");
                        xmlreader.ReadStartElement("CustomsCode", "cat_ru");
                        string custom = xmlreader.ReadString();
                        xmlreader.ReadEndElement();
                        xmlreader.ReadEndElement();
                        xmlreader.ReadEndElement();
                    }