[HttpGet]
 [ProducesResponseType(typeof(FileResult), 200)]
 public IActionResult downloadfile()
 {         
     var FilePath = FHostingEnvironment.WebRootPath + "\\abc.apk";
     var fileinfo= FHostingEnvironment.ContentRootFileProvider.GetFileInfo(FilePath);
     var stream = new FileStream(FilePath, FileMode.Open,FileAccess.Read,FileShare.ReadWrite);           

     return File(stream, "application/octet-stream", "abc.apk");
 }