docs: public static void splitPdf(String inputPdfFile, String outputPdfFile, String firstPage, String lastPage) {
          if (firstPage.trim().isEmpty()) {
              firstPage = "0";
          }
          if (lastPage.trim().isEmpty()) {
              lastPage = "0";
          }
  
          splitPdf(new File(inputPdfFile), new File(outputPdfFile), Integer.parseInt(firstPage), Integer.parseInt(lastPage));
      }