Create PDF in memory instead of physical file

How do one create PDF in memorystream instead of physical file using itextsharp.

The code below is creating actual pdf file.

Instead how can I create a byte[] and store it in the byte[] so that I can return it through a function

using iTextSharp.text;
using iTextSharp.text.pdf;
Document doc = new Document(iTextSharp.text.PageSize.LETTER, 10, 10, 42, 35);
PdfWriter wri = PdfWriter.GetInstance(doc, new FileStream("c:\\Test11.pdf", FileMode.Create));
doc.Open();//Open Document to write
Paragraph paragraph = new Paragraph("This is my first line using Paragraph.");
Phrase pharse = new Phrase("This is my second line using Pharse.");
Chunk chunk = new Chunk(" This is my third line using Chunk.");

doc.Add(paragraph);

doc.Add(pharse);

doc.Add(chunk);
doc.Close(); //Close document