try{
            PdfReader pdfReader1 = new PdfReader("firstFile.pdf");
            PdfReader pdfReader2 = new PdfReader("secondFile.pdf");
            PdfCopyFields finalCopy = new PdfCopyFields(new FileOutputStream("finalCopy.pdf"));
            finalCopy.open();
            [pdfReader1,pdfReader2].each {PdfReader pdfReader ->
                   finalCopy.addDocument(pdfReader);
            }
            finalCopy.close();
        } catch (DocumentException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }