我想签名已经包含签名域的PDF。我需要添加新的签名域，保留现有的未签名的签名域。签名此类PDF后，我发现通过代码添加的新签名域始终无效。显示“文档已更改”。
下面的代码用于计算文档的哈希：

private DocumentSignatureStructure createSignatureStructureAndComputeHash(byte[] inputFile, File tempFile,
                                                                              SignatureProperties sigProperties)
            throws IOException, NoSuchAlgorithmException {

        try (FileOutputStream fos = new FileOutputStream(tempFile);
             PDDocument doc = PDDocument.load(inputFile);
             SignatureOptions signatureOptions = new SignatureOptions();) {

            signatureOptions.setPreferredSignatureSize(SignatureOptions.DEFAULT_SIGNATURE_SIZE * 2);
            signatureOptions.setPage(sigProperties.getPage() - 1);
            if (sigProperties.isVisibleSignature()) {
                PDRectangle rect = createSignatureRectangle(doc, sigProperties);
                signatureOptions.setVisualSignature(createVisualSignatureTemplate(doc, rect, sigProperties));
            }

            PDSignature signature = new PDSignature();
            signature.setFilter(PDSignature.FILTER_ADOBE_PPKLITE);
            signature.setSubFilter(PDSignature.SUBFILTER_ADBE_PKCS7_DETACHED);
            signature.setSignDate(Calendar.getInstance());
            doc.addSignature(signature, signatureOptions);
            ExternalSigningSupport externalSigning = doc.saveIncrementalForExternalSigning(fos);

            MessageDigest digest = MessageDigest.getInstance(sigProperties.getHashAlgorithm().getAlgoName());
            byte[] hashBytes = digest.digest(IOUtils.toByteArray(externalSigning.getContent()));
            String base64Hash = Base64.toBase64String(hashBytes);
            externalSigning.setSignature(new byte[0]);
            int offset = signature.getByteRange()[1] + 1;
            IOUtils.closeQuietly(signatureOptions);
            return DocumentSignatureStructure.builder().offset(offset)
                    .hashValue(base64Hash)
                    .build();
        }
    }

嵌入签名代码：

byte[] originalDocumentByte = docBlob.getBytes(1L, (int) docBlob.length());
            File file = new File(getTempFolderPath(), getTempFileName("signed"));
            try (FileOutputStream fos = new FileOutputStream(file);) {
                fos.write(originalDocumentByte);
            }
            try (RandomAccessFile raf = new RandomAccessFile(file, "rw")) {
                raf.seek(documentSignatureStructure.getOffset());
                raf.write(Hex.getBytes(Base64.decode(encodedSignature)));
            }
            Blob signedAndLtvBlob;
            try (PDDocument doc = PDDocument.load(file);
                 FileOutputStream fos = new FileOutputStream(file);
                 FileInputStream fis = new FileInputStream(file)) {
                if (createDss) {
                    log.info("Adding revocation information to DSS dictionary of PDF");
                    makeLtv(doc, revocationData);
                }
                doc.saveIncremental(fos);
            }

它不适用于上述代码。
在Google上搜索，发现COSObject 'NeedToBeUpdated'标志需要设置为true的解决方案很少。在上述代码中添加新签名字段之前，添加了以下代码块。

//..
if (sigProperties.isVisibleSignature()) {
                PDRectangle rect = createSignatureRectangle(doc, sigProperties);
                signatureOptions.setVisualSignature(createVisualSignatureTemplate(doc, rect, sigProperties));
            }

            PDAcroForm acroForm = doc.getDocumentCatalog().getAcroForm();
            COSDictionary catalogDictionary = doc.getDocumentCatalog().getCOSObject();
            catalogDictionary.setNeedToBeUpdated(true);
            COSDictionary acroFormDictionary = (COSDictionary) catalogDictionary.getDictionaryObject(COSName.ACRO_FORM);
            acroFormDictionary.setNeedToBeUpdated(true);
            COSArray array = (COSArray) acroFormDictionary.getDictionaryObject(COSName.FIELDS);
            array.setNeedToBeUpdated(true);
            for (PDField field : acroForm.getFieldTree()) {
                if (field instanceof PDSignatureField) {
                    COSDictionary fieldDictionary = field.getCOSObject();
                    COSDictionary dictionary = (COSDictionary) fieldDictionary.getDictionaryObject(COSName.AP);
                    dictionary.setNeedToBeUpdated(true);
                    COSStream stream = (COSStream) dictionary.getDictionaryObject(COSName.N);
                    stream.setNeedToBeUpdated(true);
                    while (fieldDictionary != null)
                    {
                        fieldDictionary.setNeedToBeUpdated(true);
                        fieldDictionary = (COSDictionary) fieldDictionary.getDictionaryObject(COSName.PARENT);
                    }
                }
            }
            
            PDSignature signature = new PDSignature();
            signature.setFilter(PDSignature.FILTER_ADOBE_PPKLITE);
            signature.setSubFilter(PDSignature.SUBFILTER_ADBE_PKCS7_DETACHED);
//..

即使这样也不起作用。
生成的PDF显示签名无效：

用于签名的PDF，签名域为：

我在这里漏掉了什么？
PDF文件：https://drive.google.com/file/d/1-vu9_WIfFo198v6AxoBMxCuyX1rE2FOS/view?usp=share_link
签名的PDF（无效）：https://drive.google.com/file/d/1DD0aKVkonH9a_CfGrj9mACe6DBt4Ijsj/view?usp=share_link