PDF下载链接不正常

我正在制作一个Android应用程序与MySQL数据库。我做了一个PDF报告，点击一个按钮就可以下载。我在安卓设备的谷歌浏览器中使用了这个链接，效果很好。当我试图在我的应用程序中使用相同的链接时，它似乎不工作。到目前为止，我所做的是希望通过单击按钮下载该文件。我有以下代码:

public class MainActivity extends ActionBarActivity {
private Button button;
private String LOGIN_URL =
        "http://amjad-test.site40.net/arabictest.php";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    button = (Button) findViewById(R.id.mybutton) ;
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(LOGIN_URL));
            request.setTitle("File Downloading");
            request.setDescription("File is being Downloaded...");
            request.allowScanningByMediaScanner();
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE);
            String File_name = URLUtil.guessFileName(LOGIN_URL, null, MimeTypeMap.getFileExtensionFromUrl(LOGIN_URL));
            request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, File_name);
            DownloadManager manager = (DownloadManager) MainActivity.this.getSystemService(Context.DOWNLOAD_SERVICE);
            manager.enqueue(request);
            Toast.makeText(MainActivity.this, "Downloading", Toast.LENGTH_LONG).show();

        }
    });
   }