You need to use a font that contains glyphs for those characters. If you search the mailing list archives, you'll find lots of examples of this. The basic pattern is to register the font with ITextFontResolver or @font-face and then reference the font in your CSS with font-family.
Pete
DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
Document doc = builder.parse(new StringBufferInputStream(buf.toString()));
ITextRenderer renderer = new ITextRenderer();
renderer.setDocument(doc, null);
String outputFile = "100bottles.pdf";
OutputStream os = new FileOutputStream(outputFile);
renderer.layout();
renderer.createPDF(os);
os.close();
http://groups.google.com/group/flying-saucer-users/browse_thread/thread/63d5ec6be2f034c6
Pete