HTML encoded characters and CDATA being lost after converting xml String to Document object then back to String. Is there any way to avoid?

Lets say we have an xml like so:

<item>
   <![CDATA[abc]]>
</item>

I have a method convertStringToDocument that converts this String xmlString into a Document (org.w3c.dom.Document). In order to digitally sign the xml.

public static Document convertStringToDocument(String xmlString) {
    try {
        DocumentBuilder db = generateDocumentBuilder();
        Document document = db.parse(new InputSource(new StringReader(xmlString)));
        retu document;
    } 
    catch ...
    }
    retu null;
}

public static DocumentBuilder generateDocumentBuilder() {
    try {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        dbf.setNamespaceAware(true);
        dbf.setIgnoringElementContentWhitespace(false);
        dbf.setIgnoringComments(false);
        dbf.setFeature("http://xml.org/sax/features/exteal-general-entities", false);
        dbf.setFeature("http://xml.org/sax/features/exteal-parameter-entities", false);
        DocumentBuilder db = dbf.newDocumentBuilder();
        retu db;
    } 
    catch ...
    }
    retu null;
}

However, when converting this Document back into a string, the <![CDATA[ ... ]]> tag is lost. The same this occurs for html encoded characters like –. Below is how Document objects are converted back to string:

public static String convertDocumentToString(Document doc, boolean omitXmlDeclaration) {
    try {
        StringWriter sw = new StringWriter();
        TransformerFactory tf = TransformerFactory.newInstance();
        Transformer t = tf.newTransformer();
        t.setOutputProperty(OutputKeys.METHOD, "xml");
        t.setOutputProperty(OutputKeys.INDENT, "no");
        t.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
        t.transform(new DOMSource(doc), new StreamResult(sw));
        retu sw.toString();
    } 
    catch ...
    }
    retu null;
}

Is it possible to convert the String xmlString into a Document and then back into a String without losing <![CDATA[...]]> tags or HTML encoding?