code: protected function execute(Command $command)
      {
          $command->setJar($this->getPathToPdfBox());
          $command->setOptions($this->_options);
          exec((string) $command . ' 2>&1', $stdErr, $exitCode);
          if ($command->getPdfFileIsTemp()) {
              unlink($command->getPdfFile());
          }
          if ($exitCode > 0) {
              throw new \RuntimeException(join("\n", $stdErr), $exitCode);
          }
          $resultFile = $command->getTextFile();
          $result = file_get_contents($resultFile);
          if ($command->getTextFileIsTemp()) {
              unlink($resultFile);
          }
          return $result;
      }
docs: Execute given Command object.
  
  @param Command $command
  @throws \RuntimeException If PdfBox returns error exit code
  @return string            The converted text or HTML as string