code: def render_pdf_file_to_image_files_pdftoppm_ppm(pdf_file_name, root_output_file_path,
                                             res_x=150, res_y=150, extra_args=None):
      
  
      if extra_args is None: extra_args = []
  
      if not pdftoppm_executable:
          init_and_test_pdftoppm_executable(prefer_local=False, exit_on_fail=True)
  
      if old_pdftoppm_version:
          # We only have -r, not -rx and -ry.
          command = [pdftoppm_executable] + extra_args + ["-r", res_x, pdf_file_name,
                                                root_output_file_path]
      else:
          command = [pdftoppm_executable] + extra_args + ["-rx", res_x, "-ry", res_y,
                                                pdf_file_name, root_output_file_path]
      comm_output = get_external_subprocess_output(command)
      return comm_output
docs: Use the pdftoppm program to render a PDF file to .png images.  The
      root_output_file_path is prepended to all the output files, which have numbers
      and extensions added.  Extra arguments can be passed as a list in extra_args.
      Return the command output.