// ms is a memory stream 

PdfForms forms = new PdfForms();
PdfDocument doc = PdfDocument.Load(ms, forms);

foreach(int pageIndex in listOfPageIndexes)
{
     PdfForms formsDup = new PdfForms();
     PdfDocument docDup;

     // ms2 is a memory stream
     docDup = PdfDocument.Load(ms2, formsDup);

      //This renames the fields so that it can be added with conflicting with the previous document. 

      foreach (var field in docDup.FormFill.InterForm.Fields.ToList())
      {
         string fieldName = field.Dictionary.FirstOrDefault(u => u.Key.StartsWith("T")).Value.As<PdfTypeString>().AnsiString;
         var typeString = field.Dictionary.FirstOrDefault(u => u.Key.StartsWith("T")).Value.As<PdfTypeString>();
         typeString.AnsiString = fieldName + "_" + (index + 1).ToString();
      }

     doc.Pages.ImportPages(docDup, indexToPrint.ToString(), doc.Pages.Count);
}