code: public static void renderDOTExternal(File dotFile, String format) throws IOException {
          renderDOTExternal(IOUtil.asBufferedUTF8Reader(dotFile), format);
      }
docs: Renders a GraphVIZ description from a file, using an external program for displaying. Convenience method, see
  {@link #renderDOTExternal(Reader, String)}.
  
  @throws IOException
  if opening the file resulted in errors.