How can I use several link to same file

There are a load of ways to do this, starting off by linking to a page that doesn't exist on your system: "mydomain.com/downloads/F543210987" and handling the 404 error. Get the filename, translate that to the actual file (probably via a DB) and serve that up as a download item.
Then there are ASHX pages which do the same thing but don't need the DB.
Or a Download.aspx file that takes a query string - I use this one.

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="FileTransferDownload.aspx.cs" Inherits="FileTransferDownload" %>

<%  
    // Send a download file to the client given the filename.    
    string guid = Request.QueryString["file"];
    string fileName = "ERROR";
    byte[] data = new byte[] { 0, 0, 0, 0 };
    string strCon = System.Web.Configuration.WebConfigurationManager.ConnectionStrings["DownloadDatabase"].ConnectionString;
    using (System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(strCon))
        {
        con.Open();
        string strcmd = "SELECT [iD] ,cn.[fileName],[description] ,[dataContent] ,[version] " +
                        "FROM dlContent cn " +

                        "WHERE cn.iD=@ID";
        using (System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand(strcmd, con))
            {
            cmd.Parameters.AddWithValue("@ID", guid);
            using (System.Data.SqlClient.SqlDataReader r = cmd.ExecuteReader())
                {
                if (r.Read())
                    {
                    fileName = (string) r["filename"];
                    data = (byte[]) r["dataContent"];
                    }
                }
            }
        }
    Response.Clear();
    Response.AddHeader("Cache-Control", "no-cache, must-revalidate, post-check=0, pre-check=0");
    Response.AddHeader("Pragma", "no-cache");
    Response.AddHeader("Content-Description", "File Download");
    Response.AddHeader("Content-Type", "application/force-download");
    Response.AddHeader("Content-Transfer-Encoding", "binary\n");
    Response.AddHeader("content-disposition", "attachment;filename=" + fileName);
    Response.BinaryWrite(data);
    //Response.WriteFile("wm5ftdata/" + fileName);
    Response.End();  
%>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

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

        }
    }