您可以在ShowSignature.javaPDFBox源代码download的examples子项目或repository中的www.example.com示例中找到显示证书链的代码。
下面是从那里精简的一些代码，这些代码仅适用于某些签名子类型（adbe.pkcs7.detached和ETSI.CAdES.detached，其他的可以在上面提到的示例中看到）：

try (PDDocument document = PDDocument.load(file))
{
    for (PDSignature sig : document.getSignatureDictionaries())
    {
        COSDictionary sigDict = sig.getCOSObject();
        COSString contents = (COSString) sigDict.getDictionaryObject(COSName.CONTENTS);
        CMSSignedData signedData = new CMSSignedData(contents.getBytes());
        Store<X509CertificateHolder> certificatesStore = signedData.getCertificates();
        JcaX509CertificateConverter certificateConverter = new JcaX509CertificateConverter();
        Collection<X509CertificateHolder> matches = certificatesStore.getMatches(null);
        System.out.println("Certificates in chain: " + matches.size());
        System.out.println();
        int n = 0;
        for (X509CertificateHolder certificateHolder : matches)
        {
            ++n;
            X509Certificate certificate = certificateConverter.getCertificate(certificateHolder);
            System.out.println("Certificate " + n + ":");
            System.out.println(certificate);
            System.out.println();
        }
    }
}

ShowSignature.java示例提供了更多功能：它检查签名的有效性、签名是否覆盖整个文档，并（2.0.13中的新功能）检查包括撤销（OCSP或CRL）在内的整个证书链。