Probably, you can't: The default permissions for the user your website is running under will almost certainly not allow you to access files in the root directory of your server, and your website cannot specify the storage location of a file on the client (or even if it is stored at all - that is up to the user)
But...this is the code I use to perform much teh same task:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="wm5ftdl.aspx.cs" Inherits="wm5ftdl" %>
<%
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.End();
%>
It retrieves the file data from a DB, but that's easy to change.