code: def change_filename(filehandle, meta):
      
      filename = secure_filename(meta.get('filename', filehandle.filename))
      basename, _ = os.path.splitext(filename)
      meta['original_filename'] = filehandle.filename
      filehandle.filename = filename + '.jpg'
      return filehandle
docs: Changes the filename to reflect the conversion from PDF to JPG.
      This method will preserve the original filename in the meta dictionary.