Download File Code

  private void DownloadFile(Int64 FileID)
    {
        objFile.Operation = "SELECTBYID";
        objFile.FileID = Convert.ToInt64(ViewState["FileID"]);
        ds = objFileDA.View_Detail(objFile);
        if (ds.Tables[0].Rows.Count > 0)
        {
            //code for download file

            string filepath = Server.MapPath(WebConfigurationManager.AppSettings.Get("strFilePath")) + ds.Tables[0].Rows[0]["MFileName"].ToString(); ;
            // Create New instance of FileInfo class to get the properties of the file being downloaded
            FileInfo file = new FileInfo(filepath);

            // Checking if file exists
            if (file.Exists)
            {
                Response.ClearContent();
                // LINE1: Add the file name and attachment, which will force the open/cance/save dialog to show, to the header
                Response.AddHeader("Content-Disposition", "attachment; filename=" + file.Name);

                // Add the file size into the response header
                Response.AddHeader("Content-Length", file.Length.ToString());

                // Set the ContentType
                Response.ContentType = ReturnExtension(file.Extension.ToLower());

                // Write the file into the response (TransmitFile is for ASP.NET 2.0. In ASP.NET 1.1 you have to use WriteFile instead)
                Response.TransmitFile(file.FullName);

                // End the response
                Response.End();
            }
            // Get the physical Path of the file(test.doc)

            //end of code
        }
    }
    private string ReturnExtension(string fileExtension)
    {
        switch (fileExtension)
        {
            case ".htm":
            case ".html":
            case ".log":
                return "text/HTML";
            case ".txt":
                return "text/plain";
            case ".doc":
                return "application/ms-word";
            case ".tiff":
            case ".tif":
                return "image/tiff";
            case ".asf":
                return "video/x-ms-asf";
            case ".avi":
                return "video/avi";
            case ".zip":
                return "application/zip";
            case ".xls":
            case ".csv":
                return "application/vnd.ms-excel";
            case ".gif":
                return "image/gif";
            case ".jpg":
            case "jpeg":
                return "image/jpeg";
            case ".bmp":
                return "image/bmp";
            case ".wav":
                return "audio/wav";
            case ".mp3":
                return "audio/mpeg3";
            case ".mpg":
            case "mpeg":
                return "video/mpeg";
            case ".rtf":
                return "application/rtf";
            case ".asp":
                return "text/asp";
            case ".pdf":
                return "application/pdf";
            case ".fdf":
                return "application/vnd.fdf";
            case ".ppt":
                return "application/mspowerpoint";
            case ".dwg":
                return "image/vnd.dwg";
            case ".msg":
                return "application/msoutlook";
            case ".xml":
            case ".sdxl":
                return "application/xml";
            case ".xdp":
                return "application/vnd.adobe.xdp+xml";
            default:
                return "application/octet-stream";
        }
    }