code: protected function prepareCommand($filename, $saveToFile, $pdfIsTemp = false)
      {
          $resultIsTemp = false;
          $command = new Command();
          $command->setPdfFile($filename, $pdfIsTemp);
          if ($saveToFile === null) {
              $saveToFile = tempnam(sys_get_temp_dir(), 'pdfbox');
              $resultIsTemp = true;
          }
          $command->setTextFile($saveToFile, $resultIsTemp);
          return $command;
      }
docs: Factory method for Command object
  
  @param string $filename   Path to input file
  @param string $saveToFile Path to output file or null if file should not be saved
  @param bool   $pdfIsTemp  True if given PDF is a temporary file. Default: false
  @return \SGH\PdfBox\Command