implementation 'com.google.zxing:core:3.4.1'
implementation 'com.google.zxing:javase:3.4.1'
implementation 'com.itextpdf:itextpdf:5.5.13.2'

public class PdfUtils {

    /*
        Add QR code to pdf bytes
     */
    public static byte[] addQRCode(byte[] pdfBytes, String barcodeText, QRCodePosition position) {
        try (ByteArrayOutputStream os = new ByteArrayOutputStream()) {
            PdfReader reader = new PdfReader(pdfBytes);
            PdfStamper stamper = new PdfStamper(reader, os);
            Image image = Image.getInstance(newQRCodeImage(barcodeText));
            for (int i = 1; i <= reader.getNumberOfPages(); i++) {
                PdfContentByte content = stamper.getOverContent(i);
                image.setAbsolutePosition(position.getAbsoluteX(), position.getAbsoluteY());
                content.addImage(image);
            }
            stamper.close();
            reader.close();
            return os.toByteArray();
        } catch (DocumentException | IOException e) {
            throw new RuntimeException("Error on writing QR code", e);
        }
    }

    /*
        Get new QR code image bytes for barcode text
    */
    private static byte[] newQRCodeImage(String barcodeText) {
        try (ByteArrayOutputStream image = new ByteArrayOutputStream()) {
            QRCodeWriter barcodeWriter = new QRCodeWriter();
            BitMatrix bitMatrix = barcodeWriter.encode(barcodeText, BarcodeFormat.QR_CODE, 120, 120);
            MatrixToImageWriter.writeToStream(bitMatrix, "png", image);
            return image.toByteArray();
        } catch (WriterException | IOException e) {
            throw new RuntimeException("Error on generating QR code", e);
        }
    }

    public enum QRCodePosition {
        TOP_LEFT(0f, 700f),
        TOP_RIGHT(500f, 700f),
        BOTTOM_LEFT(0f, 0f),
        BOTTOM_RIGHT(500f, 0f);

        private final float absoluteX;
        private final float absoluteY;

        QRCodePosition(float absoluteX, float absoluteY) {
            this.absoluteX = absoluteX;
            this.absoluteY = absoluteY;
        }

        public float getAbsoluteX() {
            return absoluteX;
        }
        
        public float getAbsoluteY() {
            return absoluteY;
        }
    }
}