UnsignXMLDocument.cs

/// <summary>
/// Remove the Signature from signed XML document
/// </summary>
/// <param name="xmlFilePath">Path to the signed xml document</param>
/// <returns>The unsigned xml document</returns>
private static XmlDocument UnsignXMLDocument(string xmlFilePath)
{
    var xmlDocument = ReadXMLDocumentFromPath(xmlFilePath);

    var nodeList = xmlDocument.GetElementsByTagName("Signature");

    xmlDocument.DocumentElement.RemoveChild(nodeList[0]);

    return xmlDocument;
}