docs: public static void mergePdf(File[] inputPdfFiles, File outputPdfFile) {
          if (PDFBOX.equals(System.getProperty(PDF_LIBRARY))) {
              PdfBoxUtilities.mergePdf(inputPdfFiles, outputPdfFile);
          } else {
              try {
                  PdfGsUtilities.mergePdf(inputPdfFiles, outputPdfFile);
              } catch (Exception e) {
                  System.setProperty(PDF_LIBRARY, PDFBOX);
                  mergePdf(inputPdfFiles, outputPdfFile);
              }
          }
      }