How to Remove default underscore in asp.net while downloading the file - asp.net

Question

protected void DownloadFile(object sender, EventArgs e)
{
string param = Request.QueryString["id"];
//int id = int.Parse((sender as LinkButton).CommandArgument);
//byte[] bytes;
string fileName;
SqlCommand cd = DbCon._dbConnection.CreateCommand();
cd.CommandType = CommandType.Text;
cd.CommandText = "select id from student_registration where id = '" + param + "'";
cd.ExecuteNonQuery();
SqlCommand cmd = DbCon._dbConnection.CreateCommand();
cmd.CommandText = "select books_pdf from books where id = '" + param + "'";
// cmd.Parameters.AddWithValue("#Id", param);
String s1 = cmd.ExecuteScalar().ToString();
using (SqlDataReader sdr = cmd.ExecuteReader())
{
sdr.Read();
//bytes = (byte[])sdr["Data"];
//contentType = sdr["ContentType"].ToString();
fileName = sdr["books_pdf"].ToString();
}
Response.Clear();
Response.Buffer = true;
Response.Charset = "/";
Response.Cache.SetCacheability(HttpCacheability.NoCache);
//Response.ContentType = contentType;
Response.ContentType = "application/pdf";
Response.AddHeader("Content-Disposition", "attachment; filename=" + fileName );
//Response.AppendHeader("Content-Disposition", "attachment; filename=" +fileName);
// Response.TransmitFile(Server.MapPath("~/Files/"+ fileName));
// Response.WriteFile(file.FullName);
Response.Flush();
Response.End();
}
This is the code where I have written to download the file. but the result what am getting correct file but '/' is replaced with 'underscore;
My question is how to remove that underscore and add '/' in place of underscore I have attached the image please check that and please help me in finding the solutionenter image description here
enter image description here
image shows the path stored in database and error what I am facing to download

Answer 1

fileName = "../librarian/" + sdr["books_pdf"].ToString();
}
WebClient req = new WebClient();
HttpResponse response = HttpContext.Current.Response;
response.Clear();
response.ClearContent();
response.ClearHeaders();
response.Buffer = true;
response.AddHeader("Content-Disposition", "attachment;filename=\"" + Server.MapPath(fileName) + "\"");
byte[] data = req.DownloadData(Server.MapPath(fileName));
response.BinaryWrite(data);
response.End();
Proper Selection of File was not given later i corrected proper file location than i got proper output