stop to open dynamically created PDF in browser

hi,
i create a pdf dynamically it's perfect but the problem is that i want to open this pdf in popup but it cant't open in popup it open direct in browser.
my code is below.
===============================================================
CLASS file
========
public class clsCreatePDF
{
    public clsCreatePDF()
    {
        //
        // TODO: Add constructor logic here
        //
    }
    public string CreatePDF(string imagename)
    {
       HttpContext.Current.Response.ContentType = "application/pdf";
        Document doc = new Document();
        string fileName = Convert.ToString(DateTime.Now.Year + DateT ...