Document document = new Document();
document.loadFromFile("Sample.docx");
Section s = document.getSections().get(0);
Paragraph para = s.getParagraphs().get(0);
//the first method
TextSelection[] textSelections = para.findAllString("The", false, true);
for (TextSelection selection : textSelections)
{
    //highlight
    selection.getAsOneRange().getCharacterFormat().setHighlightColor(new Color(255, 255, 0));
}
//the second method
Pattern c = Pattern.compile("The");
TextSelection[] textSelections = para.findAllPattern(c);
for (TextSelection selection : textSelections)
{
    TextRange[] results = selection.getAsRange();
    for (TextRange result : results)
    {
        //highlight
        result.getCharacterFormat().setHighlightColor(Color.yellow);
    }
}