Downloading Attachment using Response.AddHeader("content-disposition", attachment)

first create a excel file in your local system as well as in your project then take a download link button and write following code
protected void LinkButton1_Click(object sender, EventArgs e)
    {
        string fileName = "test.xlsx";
        string filePath = Server.MapPath("~/test.xlsx");
        Response.Clear();

        Response.AppendHeader("content-disposition", "attachment; filename=" + fileName);
        Response.ContentType = "application/octet-stream";
        Response.WriteFile(filePath);
        Response.Flush();
        Response.End();

    }

It will display like

Thanks
shibashish mohanty