签名定义。必须在 PdfSignatureAppearance 中关闭

Question

我在签署 pdf 时遇到以下错误。错误是 “签名定义。必须在 PdfSignatureAppearance 中关闭。”

我第一次能够在 pdf 上签名。它在输出文件夹中创建一个带有第一页签名的 pdf 文件。到目前为止，代码工作正常。现在，当我将最近生成的文件作为输入以登录第二页时，我收到错误“签名已定义。必须在 PdfSignatureAppearance 中关闭。”

我收到以下行中的错误

appearance.SetVisibleSignature(new iTextSharp.text.Rectangle(300, 40, 530, 120), pageNo, "Icsi-Vendor");

请在下面找到代码

if (File.Exists(fName))
{
    PdfReader.unethicalreading = true;
    using (PdfReader pdfReader = new PdfReader(fName))
    {
        //file name
       fName = fName.Substring(fName.LastIndexOf("\") + 1);
        outputFile = outputFolder + fName + ".pdf";
        if (!File.Exists(outputFile))
        {
            using (FileStream fout = new FileStream(outputFile, FileMode.Create, FileAccess.ReadWrite))
            {
                using (PdfStamper stamper = PdfStamper.CreateSignature(pdfReader, fout, '[=11=]'))
                {
                    PdfSignatureAppearance appearance = stamper.SignatureAppearance;
                    string imagePath = txtImage.Text;
                    iTextSharp.text.Image signatureFieldImage = iTextSharp.text.Image.GetInstance(imagePath);
                    appearance.SignatureGraphic = signatureFieldImage;

                    signatureFieldImage.SetAbsolutePosition(250, 50);
                    stamper.GetOverContent(pageNo).AddImage(signatureFieldImage);

                    appearance.SetVisibleSignature(new iTextSharp.text.Rectangle(300, 40, 530, 120), pageNo, "Icsi-Vendor");
                    appearance.Reason = txtReason.Text;

                    IExternalSignature es = new PrivateKeySignature(pk, "SHA-256");
                    MakeSignature.SignDetached(appearance, es, new X509Certificate[] { pk12.GetCertificate(alias).Certificate }, null, null, null, 0, CryptoStandard.CMS);
                    stamper.Close();
                }
            }
        }
    }
    this.Invoke(new BarDelegate(UpdateBar), fName);
}

有人可以帮助我吗？如果需要更多详细信息，请告诉我。

Answer 1

OP 的代码中存在多个问题：

正确的关闭调用

应用签名时，不能关闭压模对象本身，而是关闭签名外观对象。如果使用像 MakeSignature.SignDetached 这样的辅助方法，甚至不必编写关闭代码，因为 SignDetached 已经隐式关闭了最后一行的 appearance。

因此，请

删除 stamper.Close() 和
不要将 PdfStamper stamper = PdfStamper.CreateSignature(pdfReader, fout, '[=18=]') 放入 using 指令中，因为这会导致调用压模的 Dispose 方法，后者又会调用 Close.

通常你不会被这些行伤害，因为在 MakeSignature.SignDetached 中的隐式外观 close 之后，进一步的 close 调用将被忽略。

不过，如果你没有做到这一点，例如由于之前的一些错误情况，此类关闭调用会导致您观察到错误，在您的情况下，关闭调用是由 using 指令引起的。

SetVisibleSignature 中的问题

您遇到了

中的错误

appearance.SetVisibleSignature(new iTextSharp.text.Rectangle(300, 40, 530, 120), pageNo, "Icsi-Vendor");

不幸的是，由于 using 指令，在 Dispose 调用期间，此行中发生的实际错误被替换为 Close 调用引起的错误。

考虑消息代码：

/**
 * Sets the signature to be visible. It creates a new visible signature field.
 * @param pageRect the position and dimension of the field in the page
 * @param page the page to place the field. The fist page is 1
 * @param fieldName the field name or <CODE>null</CODE> to generate automatically a new field name
 */
virtual public void SetVisibleSignature(Rectangle pageRect, int page, String fieldName) {
    if (fieldName != null) {
        if (fieldName.IndexOf('.') >= 0)
            throw new ArgumentException(MessageLocalization.GetComposedMessage("field.names.cannot.contain.a.dot"));
        AcroFields af = writer.GetAcroFields();
        AcroFields.Item item = af.GetFieldItem(fieldName);
        if (item != null)
            throw new ArgumentException(MessageLocalization.GetComposedMessage("the.field.1.already.exists", fieldName));
        this.fieldName = fieldName;
    }
    if (page < 1 || page > writer.reader.NumberOfPages)
        throw new ArgumentException(MessageLocalization.GetComposedMessage("invalid.page.number.1", page));
    this.pageRect = new Rectangle(pageRect);
    this.pageRect.Normalize();
    rect = new Rectangle(this.pageRect.Width, this.pageRect.Height);
    this.page = page;
}

明显的原因是

带点的字段名，
文档中已存在的命名字段，或
页码无效。

正如您描述的那样

I am able to sign the pdf for the first time. It creates a pdf file in output folder with the signature in the first page. So far the code works fine. Now when I give the recently generated file as input to sign in a second page I get the error

我认为第二项是最可能的原因：如果要向同一文档添加多个签名，它们的字段名称必须不同。

附加模式

由于您表示对同一个文件应用多个签名，所以您必须使用追加模式。如果不这样做，您将使早期的签名无效：

PdfStamper stamper = PdfStamper.CreateSignature(pdfReader, fout, '[=12=]', true);

比照。 CreateSignature 方法重载评论

/**
 * Applies a digital signature to a document, possibly as a new revision, making
 * possible multiple signatures. The returned PdfStamper
 * can be used normally as the signature is only applied when closing.
 * <p>
... (outdated Java example code) ...
 * @param reader the original document
 * @param os the output stream or <CODE>null</CODE> to keep the document in the temporary file
 * @param pdfVersion the new pdf version or '[=13=]' to keep the same version as the original
 * document
 * @param tempFile location of the temporary file. If it's a directory a temporary file will be created there.
 *     If it's a file it will be used directly. The file will be deleted on exit unless <CODE>os</CODE> is null.
 *     In that case the document can be retrieved directly from the temporary file. If it's <CODE>null</CODE>
 *     no temporary file will be created and memory will be used
 * @param append if <CODE>true</CODE> the signature and all the other content will be added as a
 * new revision thus not invalidating existing signatures
 * @return a <CODE>PdfStamper</CODE>
 * @throws DocumentException on error
 * @throws IOException on error
 */
public static PdfStamper CreateSignature(PdfReader reader, Stream os, char pdfVersion, string tempFile, bool append)

签名定义。必须在 PdfSignatureAppearance 中关闭

Signature defined. Must be closed in PdfSignatureAppearance

itext

正确的关闭调用

SetVisibleSignature 中的问题

附加模式