private static void verifyPdfSignature(byte[] signedFile) throws IOException, GeneralSecurityException {
        final PdfReader pdfReader = new PdfReader(signedFile);
        final AcroFields acroFields = pdfReader.getAcroFields();

        final String signature = acroFields.getSignatureNames().stream()
                .filter(acroFields::signatureCoversWholeDocument)
                .findFirst()
                .orElseThrow(() -> new VerifySignatureException(String.format(
                        Constants.ErrorMessages.SIGNATURE_IS_MISSING)));

        final PdfPKCS7 pkcs7 = acroFields.verifySignature(signature);
        final String reason = pkcs7.getReason();
        final Calendar signedAt = pkcs7.getSignDate();
        final X509Certificate signingCertificate = pkcs7.getSigningCertificate();
        final Principal issuerDN = signingCertificate.getIssuerDN();
        final Principal subjectDN = signingCertificate.getSubjectDN();

        if (!pkcs7.verify()) {
            log.error("valid = {}, date = {}, reason = '{}', issuer = '{}', subject = '{}'",
                    false, signedAt.getTime(), reason, issuerDN, subjectDN);
            throw new VerifySignatureException(String.format(
                    Constants.ErrorMessages.VERIFY_SIGNATURE_ERROR, pkcs7.getSignName()));
        }
    }