how to create PDF file in .net , with password

public void pdf()
        {            
            int i = 0;
            // r is for random file names...
            Random r = new Random();
            i = r.Next(1, 999999999);
            string filename = i.ToString() + ".pdf";
            //path where to save...
            string path = "D:/Test/" + filename;     
            Document document = new Document();
            PdfWriter writer;
            writer = PdfWriter.GetInstance(document, new FileStream(path, System.IO.FileMode.Create));
            // Set password ...replace mypass with your password .......
            writer.SetEncryption(PdfWriter.STRENGTH128BITS, "mypass", null, PdfWriter.AllowCopy);

            document.Open();
            //document as many properties .. for time begin i am using only one ..
            //document.add is to add contant to your file..
            document.Add(new Paragraph("This document is Top Secret!"));
            document.Close();
        }