如何在新签名字段中关联以前的签名

Question

Stamper.addSignature("My Signature", 1, 20f, 10f, 100f, 100f);

Answer 1

OP希望将文档内签名可视化附加到现有签名。

首先，这显然是不允许的，如果您的文件已经认证，不允许更改

然而，令人惊讶的是，它似乎确实允许签名但未经认证的文档（示例文件就是我使用的）。

Stamper.addSignature("My Signature", 1, 20f, 10f, 100f, 100f);

使用iText 5.x，这可以使用通用的表单字段操作API来完成：

PdfReader pdfReader = new PdfReader(resource);
PdfStamper pdfStamper = new PdfStamper(pdfReader, result, '\0', true);

AcroFields acroFields = pdfStamper.getAcroFields();
for (String signatureName : acroFields.getSignatureNames())
{
    Item field = acroFields.getFieldItem(signatureName);
    field.writeToAll(PdfName.RECT, new PdfArray(new int[]{100,100,200,200}), Item.WRITE_WIDGET);
    field.markUsed(acroFields, Item.WRITE_WIDGET);

    PdfAppearance appearance = PdfAppearance.createAppearance(pdfStamper.getWriter(), 100, 100);
    appearance.setColorStroke(BaseColor.RED);
    appearance.moveTo(0, 0);
    appearance.lineTo(99, 99);
    appearance.moveTo(0, 99);
    appearance.lineTo(99, 0);
    appearance.stroke();

    PdfDictionary appDict = new PdfDictionary();
    appDict.put(PdfName.N, appearance.getIndirectReference());
    field.writeToAll(PdfName.AP, appDict, Item.WRITE_WIDGET);
}

pdfStamper.close();

(ChangeSignatureAppearance.java methodTestChangeParamese)

此代码为每个集成的PDF签名创建一个新的签名外观，在本例中是一个位于100、100和大小为100x100的红十字，但您可以在那里创建任何您喜欢的外观。

为此，您只需要稍微修改一下上面的代码：

PdfReader pdfReader = new PdfReader(resource);
PdfStamper pdfStamper = new PdfStamper(pdfReader, result, '\0', true);

AcroFields acroFields = pdfStamper.getAcroFields();
for (String signatureName : acroFields.getSignatureNames())
{
    PdfPKCS7 pkcs7 = acroFields.verifySignature(signatureName);
    X509Certificate signerCert = (X509Certificate) pkcs7.getSigningCertificate();
    String signerName = CertificateInfo.getSubjectFields(signerCert).getField("CN");

    Item field = acroFields.getFieldItem(signatureName);
    field.writeToAll(PdfName.RECT, new PdfArray(new int[]{100,100,200,200}), Item.WRITE_WIDGET);
    field.markUsed(acroFields, Item.WRITE_WIDGET);

    PdfAppearance appearance = PdfAppearance.createAppearance(pdfStamper.getWriter(), 100, 100);
    ColumnText columnText = new ColumnText(appearance);
    Chunk chunk = new Chunk();
    chunk.setSkew(0, 12);
    chunk.append("Signed by:");
    columnText.addElement(new Paragraph(chunk));
    chunk = new Chunk();
    chunk.setTextRenderMode(PdfContentByte.TEXT_RENDER_MODE_FILL_STROKE, 1, BaseColor.BLACK);
    chunk.append(signerName);
    columnText.addElement(new Paragraph(chunk));
    columnText.setSimpleColumn(0, 0, 100, 100);
    columnText.go();

    PdfDictionary appDict = new PdfDictionary();
    appDict.put(PdfName.N, appearance.getIndirectReference());
    field.writeToAll(PdfName.AP, appDict, Item.WRITE_WIDGET);
}

pdfStamper.close();

(ChangeSignatureAppearance.java方法TestChangeAppearancesWithName)

对于示例文档，BouncyCastle必须注册为security Provider。

try (   PdfReader pdfReader = new PdfReader(resource);
        PdfWriter pdfWriter = new PdfWriter(result);
        PdfDocument pdfDocument = new PdfDocument(pdfReader, pdfWriter, new StampingProperties().useAppendMode()))
{
    SignatureUtil signatureUtil = new SignatureUtil(pdfDocument);
    PdfAcroForm acroForm = PdfAcroForm.getAcroForm(pdfDocument, false);

    for (String name : signatureUtil.getSignatureNames())
    {
        PdfFormField field = acroForm.getField(name);
        field.setModified();
        for (PdfWidgetAnnotation pdfWidgetAnnotation : field.getWidgets())
        {
            pdfWidgetAnnotation.setRectangle(new PdfArray(new int[]{100, 100, 200, 200}));

            PdfFormXObject form = new PdfFormXObject(new Rectangle(100, 100));
            PdfCanvas canvas = new PdfCanvas(form, pdfDocument);
            canvas.setStrokeColor(Color.RED);
            canvas.moveTo(0, 0);
            canvas.lineTo(99, 99);
            canvas.moveTo(0, 99);
            canvas.lineTo(99, 0);
            canvas.stroke();

            pdfWidgetAnnotation.setNormalAppearance(form.getPdfObject());
        }
    }
}

与上面的iText5代码相同的警告适用：

注意：这段代码假设隐形签名已经与某个文档页面相关联。

带有主题名称的变体如下所示：

try (   PdfReader pdfReader = new PdfReader(resource);
        PdfWriter pdfWriter = new PdfWriter(result);
        PdfDocument pdfDocument = new PdfDocument(pdfReader, pdfWriter, new StampingProperties().useAppendMode()))
{
    SignatureUtil signatureUtil = new SignatureUtil(pdfDocument);
    PdfAcroForm acroForm = PdfAcroForm.getAcroForm(pdfDocument, false);

    for (String name : signatureUtil.getSignatureNames())
    {
        PdfPKCS7 pkcs7 = signatureUtil.verifySignature(name);
        X509Certificate signerCert = (X509Certificate) pkcs7.getSigningCertificate();
        String signerName = CertificateInfo.getSubjectFields(signerCert).getField("CN");
        PdfFormField field = acroForm.getField(name);
        field.setModified();
        for (PdfWidgetAnnotation pdfWidgetAnnotation : field.getWidgets())
        {
            pdfWidgetAnnotation.setRectangle(new PdfArray(new int[]{100, 100, 200, 200}));

            PdfFormXObject form = new PdfFormXObject(new Rectangle(100, 100));
            Canvas canvas = new Canvas(form, pdfDocument);
            canvas.add(new Paragraph().setItalic().add("Signed by:"));
            canvas.add(new Paragraph().setBold().add(signerName));

            pdfWidgetAnnotation.setNormalAppearance(form.getPdfObject());
        }
    }
}

关于未签名更改的警告是正确的，但再次签名后，甚至该警告也消失了：

具有签名者名称的变体如下所示：

该行动在评论中问道

try (   PdfReader pdfReader = new PdfReader(resource);
        PdfWriter pdfWriter = new PdfWriter(result);
        PdfDocument pdfDocument = new PdfDocument(pdfReader, pdfWriter, new StampingProperties().useAppendMode()))
{
    SignatureUtil signatureUtil = new SignatureUtil(pdfDocument);
    PdfAcroForm acroForm = PdfAcroForm.getAcroForm(pdfDocument, false);

    for (String name : signatureUtil.getSignatureNames())
    {
        PdfPKCS7 pkcs7 = signatureUtil.verifySignature(name);
        X509Certificate signerCert = (X509Certificate) pkcs7.getSigningCertificate();
        String signerName = CertificateInfo.getSubjectFields(signerCert).getField("CN");
        PdfFormField field = acroForm.getField(name);
        field.setModified();

        Rectangle rectangle = new Rectangle(100, 100);
        PdfFormXObject form = new PdfFormXObject(rectangle);
        Canvas canvas = new Canvas(form, pdfDocument);
        canvas.add(new Paragraph().setItalic().add("Signed by:"));
        canvas.add(new Paragraph().setBold().add(signerName));

        for (PdfWidgetAnnotation pdfWidgetAnnotation : field.getWidgets())
        {
            PdfDictionary pageObject = pdfWidgetAnnotation.getPageObject();
            PdfPage page = pdfDocument.getPage(pageObject);
            page.removeAnnotation(pdfWidgetAnnotation);

            pdfWidgetAnnotation.releaseFormFieldFromWidgetAnnotation();
        }

        for (int pageNumber = 1; pageNumber <= pdfDocument.getNumberOfPages(); pageNumber++)
        {
            PdfPage pdfPage = pdfDocument.getPage(pageNumber);
            PdfWidgetAnnotation pdfWidgetAnnotation = new PdfWidgetAnnotation(rectangle);
            pdfWidgetAnnotation.setNormalAppearance(form.getPdfObject());
            pdfWidgetAnnotation.setPage(pdfPage);
            field.addKid(pdfWidgetAnnotation);
            pdfPage.addAnnotation(pdfWidgetAnnotation);
        }
    }
}

这首先删除签名字段的任何现有注释，然后向所有字段添加新注释。

就像上面一样，这会出现一个关于未签名更改的警告，毕竟这是真的。

顺便说一句，如果在一个页面上使用带有可视化的签名文档，并更改上面的代码以不删除原始注释，则可以很容易地将该注释的副本添加到所有页面，而当前的Adobe Acrobat Reader甚至不会显示警告！检查签名文档中更改的阅读器代码确实很奇怪...