display PDF document

I'm trying to following the example in http://www.beansoftware.com/ASP.NET-Tutorials/PDF-View-Custom-Control.aspx
but not quite understand it.

If I create a solution with PdfViewer project,
1) under that project, there's Properties folder. Do I need to add any file to that folder?

2) I think it adds ShowPdf.cs (the custom control) file to the project (the file is placed outside the Properties folder). 
   I thought a custom control should have filename extension of .ascx then why is it .cs?

   The content of ShowPdf.cs file is:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Text;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace PdfViewer
{
    [DefaultProperty("FilePath&quo ...