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

I am having trouble adding xml document (CitationDocumentBatch) that is in this object objXMLInputDoc into another object objXMLCopyOfOriginalInputDoc. It should be added as a child of <soapenv:Body>

objXMLInputDoc object contains the following

Code:

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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>

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objXMLCopyOfOriginalInputDoc contains the following

Code:

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<?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>

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

Code:

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<?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>

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Here is what I have tried.

Code:

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

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

Code:

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

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