Android itextpdf，JPEG到PDF（JPEG在PDF中显示断开）

我正在尝试从现有的JPEG图像生成PDF，但未能成功，PDF是用损坏的JPEG图像生成的，只有JPEG的前1/4是PDF

下面是我的代码

 public void createPDFFromBitmap(Bitmap bitmap){
        File appDir =  new File(Environment.getExternalStorageDirectory()+File.separator+getResources().getString(R.string.app_name));
        appDir.mkdir();

        String imageFile = appDir.getAbsolutePath() + File.separator+ "history.jpeg"; // add permission in your manifest...
        String pdfFile = appDir.getAbsolutePath() + File.separator+ "history.pdf"; // add permission in your manifest...

        File mPdfFile = new File(pdfFile);
        if(mPdfFile.exists()){
            mPdfFile.delete();
        }

        try
        {
            OutputStream os = new BufferedOutputStream(new FileOutputStream(imageFile));
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, os);
            os.close();

            Document document = new Document();
            PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream(pdfFile));
            document.open();
            Image image = Image.getInstance(imageFile);
            document.add(image);
            document.close();
            writer.close();
            shareViaEmail(mPdfFile);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

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我首先创建JPEG，然后使用该JPEG文件路径并希望将其转换为PDF，但不幸的是无法正确生成PDF，我已通过以下代码成功地生成了

Image image = Image.getInstance(imageFile);
document.setPageSize(image);
document.newPage();
image.setAbsolutePosition(0, 0);
document.add(image);