To get the namespace working, you need to use XmlNamespaceManager
.
XmlDocument myDoc = new XmlDocument();
myDoc.Load(@"Form.xml");
XmlNamespaceManager xmlNsMgr = new XmlNamespaceManager(myDoc.NameTable);
xmlNsMgr.AddNamespace("my", myDoc.DocumentElement.NamespaceURI);
XmlNodeList nl = myDoc.SelectNodes("//my:Attachment", xmlNsMgr);
With this, nl
will be populated.