I know how to extract all marks I have added in my PdfDocument.
For that, I parse the document dictionnary:  
for( int i=0; i < reader.XrefSize; i++) {           
  var obj = reader.GetPdfObject(i);
  if (obj != null && obj.GetType() == typeof(PdfDictionary) ) {
    PdfDictionary objDic = (iTextSharp.text.pdf.PdfDictionary) obj;
Now I can locate PdfName.DEST fields in these PdfDictionary:  
if (objDic.Keys.Contains(PdfName.DEST) == true) {                       
  var next = objDic.Get(PdfName.DEST);
    if (next.GetType() == typeof(PdfArray)) {
But, how to convert this next in PdfDestination ?
And how to get the 'vertical position', and better the 'page number' in the document ?
Best regards.