code: def is_pdf(document):
      
      if not executable_exists('pdftotext'):
          current_app.logger.warning(
              "GNU file was not found on the system. "
              "Switching to a weak file extension test."
          )
          if document.lower().endswith(".pdf"):
              return True
          return False
  
      # Tested with file version >= 4.10. First test is secure and works
      # with file version 4.25. Second condition is tested for file
      # version 4.10.
      file_output = os.popen('file ' + re.escape(document)).read()
      try:
          filetype = file_output.split(":")[-1]
      except IndexError:
          current_app.logger.error(
              "Your version of the 'file' utility seems to be unsupported."
          )
          raise IncompatiblePDF2Text('Incompatible pdftotext')
  
      pdf = filetype.find("PDF") > -1
      # This is how it should be done however this is incompatible with
      # file version 4.10.
      # os.popen('file -bi ' + document).read().find("application/pdf")
      return pdf
docs: Check if a document is a PDF file and return True if is is.