docs: public static void mergePdf(File[] inputPdfFiles, File outputPdfFile) {
          try {
              PDFMergerUtility mergerUtility = new PDFMergerUtility();
              mergerUtility.setDestinationFileName(outputPdfFile.getPath());
              for (File inputPdfFile : inputPdfFiles) {
                  mergerUtility.addSource(inputPdfFile);
              }
              mergerUtility.mergeDocuments(MemoryUsageSetting.setupMainMemoryOnly());
          } catch (IOException ioe) {
              logger.error("Error counting PDF pages => " + ioe);
          }
      }