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在 C# 和 VB.NET 中验证 PDF 签名

Bit Miracle 的方形标志
由 Bit Miracle 翻译。原文作者：Vitaliy Shibaev
更新于 2026年6月26日

PDF 文档中的数字签名可用于检测 PDF 是否被篡改。您可以使用 Docotic.Pdf library 在 PDF 文件中验证数字签名。该库可以帮助您在 .NET Framework 和 .NET Core 应用程序中读取签名属性。请在 下载 C# .NET PDF 库 页面获取该库和免费的限时许可证密钥。

验证 PDF 中的数字签名

使用 C# 验证 PDF 中的数字签名

Docotic.Pdf 库提供了用于检查文档签名部分在签名后是否被更改的手段。您可以检查签名是否包含嵌入的 OCSP 和/或 CRL 数据。对于任何签名，还可以检查其签名证书在给定日期是否已吊销。

下面的 C# 示例演示如何验证 PDF 签名并检查签名证书的吊销状态：

using BitMiracle.Docotic.Pdf;

using var pdf = new PdfDocument("signed.pdf");
Console.WriteLine("Verification result:");

PdfControl? field = pdf.GetControls().FirstOrDefault(c => c.Type == PdfWidgetType.Signature);
if (field is null)
{
    Console.WriteLine("Document does not contain signature fields");
    return;
}

PdfSignature? signature = ((PdfSignatureField)field).Signature;
if (signature is null)
{
    Console.WriteLine("Signature field does not have an associated signature");
    return;
}

PdfSignatureContents contents = signature.Contents;
Console.WriteLine("Signed part is intact: {0}", contents.VerifyDigest());

DateTime signingTime = signature.SigningTime ?? DateTime.MinValue;
Console.WriteLine("Signed on: {0}\n", signingTime.ToShortDateString());

if (contents.CheckHasEmbeddedOcsp())
{
    Console.WriteLine("Signature has OCSP embedded.");
    CheckRevocation(signature, PdfCertificateRevocationCheckMode.EmbeddedOcsp);
}

if (contents.CheckHasEmbeddedCrl())
{
    Console.WriteLine("Signature has CRL embedded.");
    CheckRevocation(signature, PdfCertificateRevocationCheckMode.EmbeddedCrl);
}

CheckRevocation(signature, PdfCertificateRevocationCheckMode.OnlineOcsp);
CheckRevocation(signature, PdfCertificateRevocationCheckMode.OnlineCrl);

var timestampToken = contents.GetTimestampToken();
if (timestampToken != null)
{
    Console.WriteLine("Signature has timestamp embedded.");
    Console.WriteLine("Embedded timestamp: {0}", timestampToken.GenerationTime);

    if (timestampToken.TimestampAuthority != null)
        Console.WriteLine("Timestamp authority: {0}", timestampToken.TimestampAuthority.Name);

    Console.WriteLine("Timestamp is intact: {0}", contents.VerifyTimestamp());
}

private static void CheckRevocation(PdfSignature signature, PdfCertificateRevocationCheckMode mode)
{
    PdfSignatureContents contents = signature.Contents;
    DateTime signingTime = signature.SigningTime ?? DateTime.MinValue;

    foreach (DateTime time in new DateTime[] { signingTime, DateTime.UtcNow })
    {
        bool revoked = contents.CheckIfRevoked(mode, time);
        string status = revoked ? "Revoked" : "Valid";
        string date = time.ToShortDateString();
        Console.WriteLine("Checking using {0} mode: {1} on {2}", mode, status, date);
    }
}

在 GitHub 上，您可以下载并试用完整的 验证 PDF 签名 C# 和 VB.NET 示例。

在 C# 中读取 PDF 签名属性

Docotic.Pdf 可以读取签名属性，例如签名者姓名、签名时间和签名者联系信息。也可以访问嵌入在签名中的签名证书。如果签名中嵌入了颁发者证书，库还可以检索该签名证书的颁发者证书。

本示例展示如何在 C# 中读取签名及其对应证书的属性：

using var pdf = new PdfDocument("signed.pdf");
PdfControl? control = pdf.GetControls().FirstOrDefault(c => c.Type == PdfWidgetType.Signature);
if (control is null)
{
    Console.WriteLine("Document does not contain signature fields");
    return;
}

PdfSignatureField field = (PdfSignatureField)control;
Console.WriteLine("Signature field is invisible: {0}", IsInvisible(field));

PdfSignature? signature = field.Signature;
if (signature is null)
{
    Console.WriteLine("Signature field does not have an associated signature");
    return;
}

Console.WriteLine("Signed by: {0}", signature.Name);
Console.WriteLine("Signing time: {0}", signature.SigningTime);
Console.WriteLine("Signed at: {0}", signature.Location);
Console.WriteLine("Reason for signing: {0}", signature.Reason);
Console.WriteLine("Signer's contact: {0}", signature.ContactInfo);

PdfSignatureContents contents = signature.Contents;
Console.WriteLine("Has OCSP embedded: {0}", contents.CheckHasEmbeddedOcsp());
Console.WriteLine("Has CRL embedded: {0}", contents.CheckHasEmbeddedCrl());

PdfSignatureCertificate certificate = contents.GetSigningCertificate();
Console.WriteLine("== Signing certificate:");
Console.WriteLine("Name: {0}", certificate.Name);
Console.WriteLine("Algorithm: {0}", certificate.AlgorithmName);
Console.WriteLine("Subject DN: {0}", certificate.Subject.Name);
Console.WriteLine("Issuer DN: {0}", certificate.Issuer.Name);
Console.WriteLine("Serial number: {0}", certificate.SerialNumber);
Console.WriteLine("Valid from {0} up to {1}", certificate.ValidFrom, certificate.ValidUpto);
Console.WriteLine("Timestamp Authority URL: {0}", certificate.GetTimestampAuthorityUrl());

PdfSignatureCertificate? issuer = contents.GetIssuerCertificateFor(certificate);
Console.WriteLine("== Issuer certificate:");
if (issuer == null)
{
    Console.WriteLine("The issuer certificate is not embedded");
}
else
{
    Console.WriteLine("Subject DN: {0}", issuer.Subject.Name);
    Console.WriteLine("Issuer DN: {0}", issuer.Issuer.Name);
    Console.WriteLine("Serial number: {0}", issuer.SerialNumber);
}

private static bool IsInvisible(PdfSignatureField field)
{
    return (field.Width == 0 && field.Height == 0) ||
            field.Flags.HasFlag(PdfWidgetFlags.Hidden) ||
            field.Flags.HasFlag(PdfWidgetFlags.NoView);
}

从 GitHub 下载并试用完整的 在 C# 和 VB.NET 中读取 PDF 签名属性 示例。