Reading files dynamically in C#.net

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        readFile();
    }

    private void readFile()
    {
        string Filename = "NextTextfile.txt";
        string FILENAME = Server.MapPath(Filename);
        StreamReader streamReader;
        streamReader = File.OpenText(FILENAME);
        string content = streamReader.ReadToEnd();
        lblMessage.Text = content;
        objStreamReader.Close();
    }
}