code: private void processToUnicode(){
          
          PdfObject toUni = fontDic.get(PdfName.TOUNICODE);
          if (toUni != null){
              
              try {
                  byte[] touni = PdfReader.getStreamBytes((PRStream)PdfReader.getPdfObjectRelease(toUni));
      
                  CMapParser cmapParser = new CMapParser();
                  toUnicodeCmap = cmapParser.parse(new ByteArrayInputStream(touni));
              } catch (IOException e) {
                  throw new Error("Unable to process ToUnicode map - " + e.getMessage(), e);
              }
          }
      }
docs: Parses the ToUnicode entry, if present, and constructs a CMap for it
  @since 2.1.7