code: private boolean unknownByPDFExtractor(ArrayList<ArrayList<TextPiece>> wordsByPage) {
      	ArrayList<TextPiece> wordsOfPageOne = wordsByPage.get(0); 
      	boolean isUnknownCode = false;
      	int i = 0;
      	float codeSize = 0.0f;
      	while (i<wordsOfPageOne.size()) {
      		codeSize = codeSize + Math.max(wordsOfPageOne.get(i).getXScale(), wordsOfPageOne.get(i).getFontSize());
      		i++;
      	}
      	codeSize = codeSize/(float)wordsOfPageOne.size();
      	if (codeSize<=1.2) 
      		isUnknownCode = true;
      	return(isUnknownCode);
      }
docs: Detects PDF documents encoded in unknown codes
  
  All the constant values are set based on extensive observation and experiment.
  Of course, these values still need improvement for better results.
  Machine learning methods can be used to tune these values.
  
  @param wordsByPage
  the extracted texts in the word level in a document
  @return A boolean value: true/false