PDF Stamping / PDF Watermarking

Could you provide a short sample code to perform the following?

1) Open an existing PDF on disk
2) Print "Hello World" on the footer of each existing page
3) Save the PDF to disk

Here is an example of how to append a footer to every page in an
existing document:

PDFDoc doc = new PDFDoc("in.pdf");

ElementBuilder eb = new ElementBuilder(); ElementWriter writer = new

PageIterator end = doc.PageEnd();
for (PageIterator itr=doc.PageBegin(); itr!=end; itr.Next()) {
  Element element = eb.CreateTextBegin(Font.Create(doc,
Font.StandardType1Font.e_times_roman), 64);
  element = eb.CreateTextRun("Hello World!");
  element.SetTextMatrix(1, 0, 0, 1, 20, 20); // Position the text run
  writer.WriteElement(eb.CreateTextEnd()); // Finish the block of text
  writer.End(); // Save changes

doc.Save("out.pdf", 0);

For an extended example of how to use ElementBuilder/ElementWriter,
please take a look at ElementBuilder sample project