ItextSharp using ASP.NET 2.0 C#, adding multipages

I am currently using ItextSharp to create PDF certificate on the fly using Asp.net 2.0.
It involves a pdf template with form fields that get filled and rendered on the browser.
Currently, I can create one certificate at a time. I want to change the code to create multiple
certificate but have them all in one pdf? I can't find any ItextSharp documentation on creating
multiple pages from the same template into one pdf? Can someone with ItextSharp knowledge help me?
My code is posted below (some code removed for simplicity), it might be a simple change.

   protected void CreatePDF()
{
string pdfFormFileName = String.Empty;

Response.ClearContent();
Response.ClearHeaders();
Response.ContentType = "application/pdf";


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