How to Track file download status Success/Failure

below code i got from code project which said it will indicate file download status like Success/Failure but i do not understand which line will indicate the successfully file download completed. please tell me which line tell me file download completed.
if i use the below code to download file with 5GB size then does it work or any kind of problem may occur during downloading of large file at client side. please guide. thanks
//Function for File Download in ASP.Net in C# and //Tracking the status of success/failure of Download. private bool DownloadableProduct_Tracking() { //File Path and File Name string filePath = Server.MapPath("~/ApplicationData/DownloadableProducts"); string _DownloadableProductFileName = "DownloadableProduct_FileName.pdf"; System.IO.FileInfo FileName = new System.IO.FileInfo(filePath + "\\" + _DownloadableProductFileName); FileStream myFile = new File ...