title: How to make an incremental update to a PDF
body: <p>I need to make an incremental update (add some existing pdf pages)  to an signed pdf, making the included signature still be valid (that cover the first page).</p>
  
  <p>I've seen some post's telling that is possible with PDFStamper (iTextSharp), but I'm unable to find a example out to make it append.</p>