code: def preprocess_plain_text_file(self, filename, pmid, extra_annotations):
          
          with codecs.open(filename, 'r', encoding='utf-8') as f:
              content = f.read()
              self.preprocess_plain_text_string(content, pmid,
                                                extra_annotations)
docs: Preprocess a plain text file for use with ISI reder.
  
          Preprocessing results in a new text file with one sentence
          per line.
  
          Parameters
          ----------
          filename : str
              The name of the plain text file
          pmid : str
              The PMID from which it comes, or None if not specified
          extra_annotations : dict
              Extra annotations to be added to each statement, possibly including
              metadata about the source (annotations with the key "interaction"
              will be overridden)