How do I add one xml document into another xml document?

I am having trouble adding CitationDocumentBatch element that is in this object objXMLInputDoc. I want to add it to this object objXMLCopyOfOriginalInputDoc. It should be added as a child of <soapenv:Body> inside objXMLCopyOfOriginalInputDoc


objXMLInputDoc object contains the following

CitationDocumentBatch schemaVersion="3:5" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">	<CitationDocument>		<Citation>	</CitationDocument></CitationDocumentBatch>

objXMLCopyOfOriginalInputDoc contains the following

<?xml version="1.0" encoding="utf-8"?><soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing">	<soap:Header xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">	</soap:Header>	<soapenv:Body>	<!--Add CitationDocumentBatch here-->	</soapenv:Body></soapenv:Envelope>

The result I want would be in objXMLCopyOfOriginalInputDoc which after I insert/add CitationDocumentBatch from objXMLInputDoc will look like this

<?xml version="1.0" encoding="utf-8"?><soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing">	<soap:Header xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">	</soap:Header>	<soapenv:Body>	<CitationDocumentBatch schemaVersion="3:5" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">	<CitationDocument>		<Citation>	</CitationDocument></CitationDocumentBatch>	</soapenv:Body></soapenv:Envelope>

I am trying this in vb.net but I am getting an exception "The node to be inserted is from a different document context."

objXMLCopyOfOriginalInputDoc.DocumentElement.SelectSingleNode("soap:Body", objXMLNameSpaceManager).AppendChild(objXMLInputDoc.SelectSingleNode("//CitationDocumentBatch"))

Can someone help me with this? It might be very easy but I am not able to figure it out.