function download($filename){
  if(!empty($filename)){
    // Specify file path.
    $path = ''; // '/uplods/'
    $download_file =  $path.$filename;
    // Check file is exists on given path.
    if(file_exists($download_file))
    {
      // Getting file extension.
      $extension = explode('.',$filename);
      $extension = $extension[count($extension)-1]; 
      // For Gecko browsers
      header('Content-Transfer-Encoding: binary');  
      header('Last-Modified: ' . gmdate('D, d M Y H:i:s', filemtime($path)) . ' GMT');
      // Supports for download resume
      header('Accept-Ranges: bytes');  
      // Calculate File size
      header('Content-Length: ' . filesize($download_file));  
      header('Content-Encoding: none');
      // Change the mime type if the file is not PDF
      header('Content-Type: application/'.$extension);  
      // Make the browser display the Save As dialog
      header('Content-Disposition: attachment; filename=' . $filename);  
      readfile($download_file); 
      exit;
    }
    else
    {
      echo 'File does not exists on given path';
    }

 }
}
download('tasklist.pdf');