最后，我用下面的代码解决了这个问题：

File tempFile = null;
FileOutputStream fos = null;
try {
    tempFile = File.createTempFile("tmp", dr.getId(), null);
    fos = new FileOutputStream(tempFile);
    fos.write(dr.getContent().get(0).getAttachment().getData());
} catch (Exception e) {
    e.printStackTrace();
}

Document dom = null;
try {

    PDDocument pdf = PDDocument.load(tempFile);
    PDFDomTree parser = new PDFDomTree();
    dom = parser.createDOM(pdf);

    NodeList myDivs = dom.getElementsByTagName("div");

    for (int i = 0; i < myDivs.getLength(); i++) {
        NamedNodeMap myMap = myDivs.item(i).getAttributes();
        for (int j = 0; j < myMap.getLength(); j++) {

            String nodeType = myMap.item(j).getNodeName();
            String nodeClass = myMap.item(j).getNodeValue();
            if (nodeType.compareTo("class") == 0 && nodeClass.compareTo("r") == 0) {
                myMap.removeNamedItem(myMap.item(j).getNodeName());
            }

        }
    }

} catch (Exception e) {
    e.printStackTrace();
}

return dom;