如何将生成的二维码转换成pdf文件并保存到android studio的设备中

import com.google.zxing.BarcodeFormat;
import com.google.zxing.WriterException;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.qrcode.QRCodeWriter;

...

// 生成二维码并设置给ImageView
private void generateQRCode(String content) {
    QRCodeWriter qrCodeWriter = new QRCodeWriter();
    try {
        BitMatrix bitMatrix = qrCodeWriter.encode(content, BarcodeFormat.QR_CODE, 512, 512);
        int width = bitMatrix.getWidth();
        int height = bitMatrix.getHeight();
        Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
        for (int x = 0; x < width; x++) {
            for (int y = 0; y < height; y++) {
                bitmap.setPixel(x, y, bitMatrix.get(x, y) ? Color.BLACK : Color.WHITE);
            }
        }
        imageView.setImageBitmap(bitmap);
    } catch (WriterException e) {
        e.printStackTrace();
    }
}

import com.itextpdf.text.Document;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.Image;
import com.itextpdf.text.pdf.PdfWriter;

...

// 将生成的二维码保存为PDF文件
private void saveQRCodeAsPDF(Bitmap bitmap, String filePath) {
    Document document = new Document();
    try {
        PdfWriter.getInstance(document, new FileOutputStream(filePath));
        document.open();
        Image image = Image.getInstance(bitmapToByteArray(bitmap));
        document.add(image);
        document.close();
    } catch (DocumentException | IOException e) {
        e.printStackTrace();
    }
}

// 将Bitmap转换为字节数组
private byte[] bitmapToByteArray(Bitmap bitmap) {
    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    bitmap.compress(Bitmap.CompressFormat.PNG, 100, stream);
    return stream.toByteArray();
}

// 将PDF文件保存到设备中
private void savePDFFileToDevice(String filePath) {
    File file = new File(filePath);
    try {
        InputStream inputStream = new FileInputStream(file);
        OutputStream outputStream = new FileOutputStream(Environment.getExternalStorageDirectory() + "/Documents/qr_code.pdf");
        byte[] buffer = new byte[1024];
        int length;
        while ((length = inputStream.read(buffer)) > 0) {
            outputStream.write(buffer, 0, length);
        }
        outputStream.flush();
        outputStream.close();
        inputStream.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}