XSTL Transform file to XML with C#

Question

I have to add a specific element/node for the xsl stylesheet using c# code. This is the following code that I have to add that new lines:

AppContext.SetSwitch("Switch.System.Xml.AllowDefaultResolver", true);



        var xsltransf = new XslCompiledTransform();


        var xmlMemoryDoc = new XmlDocument();
        xmlMemoryDoc.Load(new StringReader(XElement.Load(@"D:\PRJ\SPM.861\SEE PM - WEB SERVICE\3.08.1.5\Default\Env\ContentVisualisations\WD\Diagram_Content_HTML_WD_View_HierarchicalCables (1).XSLT").ToString()));


        var xmlFileDoc = new XmlDocument();
        xmlFileDoc.Load(@"D:\PRJ\SPM.861\SEE PM - WEB SERVICE\3.08.1.5\Default\Env\ContentVisualisations\WD\Diagram_Content_HTML_WD_View_HierarchicalCables (1).XSLT");



        xsltransf.Load(xmlFileDoc, new XsltSettings { EnableDocumentFunction = true }, new XmlUrlResolver());


        var contentXPathDoc = new XPathDocument(XmlReader.Create(new StringReader(XElement.Load(@"D:\PRJ\SPM.861\SEE PM - WEB SERVICE\3.08.1.5\Default\Env\ContentVisualisations\WD\WD.xml").ToString())));
        var writer = new StringWriter();
       // File.WriteAllText(@"D:\PRJ\SPM.861\result.html", writer.ToString());


        xsltransf.Transform(contentXPathDoc.CreateNavigator(), null, writer/*, @"D:\Prj\SPM\8.50\1\SEE PM - WEB SERVICE\3.07.1.7\Default\Env\ContentVisualisations\WD\out.html"*/);
        var sr = writer.ToString();

and "document" is the element that I have to add (in the original xslt there is not "document" element):