在PDF文件中使用签名
如何提取签名信息
Aspose.PDF for .NET 支持使用 PdfFileSignature 类对 PDF 文件进行数字签名。目前，也可以确定证书的有效性，但我们不能提取整个证书。可以提取的信息包括公钥、指纹和颁发者等。
为了提取签名信息，我们在 PdfFileSignature 类中引入了 ExtractCertificate(..) 方法。请查看以下代码片段，该代码演示了从 PdfFileSignature 对象中提取证书的步骤：
public static void ExtractSignatureInfo()
{
string input = _dataDir + "DigitallySign.pdf";
string certificateFileName = "extracted_cert.pfx";
using (PdfFileSignature pdfFileSignature = new PdfFileSignature())
{
pdfFileSignature.BindPdf(input);
var sigNames = pdfFileSignature.GetSignNames();
if (sigNames.Count > 0)
{
string sigName = sigNames[0];
if (!string.IsNullOrEmpty(sigName))
{
Stream cerStream = pdfFileSignature.ExtractCertificate(sigName);
if (cerStream != null)
{
using (cerStream)
{
using (FileStream fs = new FileStream(_dataDir + certificateFileName, FileMode.CreateNew))
{
cerStream.CopyTo(fs);
}
}
}
}
}
}
}
从签名字段提取图像 (PdfFileSignature)
Aspose.PDF for .NET 支持使用 PdfFileSignature 类对 PDF 文件进行数字签名，并且在签署文档时，您还可以为 SignatureAppearance 设置图像。现在该 API 还提供了提取签名信息以及与签名字段相关联的图像的功能。
为了提取签名信息，我们在 PdfFileSignature 类中引入了 ExtractImage(..) 方法。请查看以下代码片段，该代码片段演示了从 PdfFileSignature 对象中提取图像的步骤：
public static void ExtractSignatureImage()
{
using (PdfFileSignature signature = new PdfFileSignature())
{
signature.BindPdf(_dataDir + "DigitallySign.pdf");
if (signature.ContainsSignature())
{
foreach (string sigName in signature.GetSignNames())
{
string outFile = _dataDir + "ExtractImages_out.jpg";
using (Stream imageStream = signature.ExtractImage(sigName))
{
if (imageStream != null)
{
imageStream.Position = 0;
using (FileStream fs = new FileStream(outFile, FileMode.OpenOrCreate))
{
imageStream.CopyTo(fs);
}
}
}
}
}
}
}
抑制位置和原因
Aspose.PDF 功能允许灵活配置数字签名实例。PdfFileSignature 类提供了签署 PDF 文件的能力。Sign 方法的实现允许对 PDF 进行签名并将特定的签名对象传递给此类。Sign 方法包含一组用于自定义输出数字签名的属性。如果需要从结果签名中抑制某些文本属性，可以将它们留空。以下代码片段演示了如何从签名块中抑制位置和原因这两行：
public static void SupressLocationReason()
{
PdfFileSignature pdfSign = new PdfFileSignature();
pdfSign.BindPdf(_dataDir + "sample01.pdf");
// Create a rectangle for signature location
System.Drawing.Rectangle rect = new System.Drawing.Rectangle(10, 10, 300, 50);
// Set signature appearance
pdfSign.SignatureAppearance = _dataDir + "aspose-logo.png";
// Create any of the three signature types
PKCS1 signature = new PKCS1(_dataDir + "test01.pfx", "Aspose2021"); // PKCS#1
pdfSign.Sign(1, string.Empty, "test01@aspose-pdf-demo.local", string.Empty, true, rect, signature);
// Save output PDF file
pdfSign.Save(_dataDir + "DigitallySign.pdf");
}
数字签名的自定义功能
Aspose.PDF for .NET 允许数字签名的自定义功能。SignatureCustomAppearance 类的 Sign 方法实现了 6 个重载，以便您舒适地使用。例如，您可以通过 SignatureCustomAppearance 类实例及其属性值来配置结果签名。以下代码片段演示了如何从 PDF 的输出数字签名中隐藏“数字签名者”标题。
public static void CustomizationFeaturesForDigitalSign()
{
PdfFileSignature pdfSign = new PdfFileSignature();
pdfSign.BindPdf(_dataDir + "sample01.pdf");
// 创建签名位置的矩形
System.Drawing.Rectangle rect = new System.Drawing.Rectangle(10, 10, 300, 50);
// 创建三种签名类型中的任意一种
PKCS1 signature = new PKCS1(_dataDir + "test01.pfx", "Aspose2021"); // PKCS#1
SignatureCustomAppearance signatureCustomAppearance = new SignatureCustomAppearance
{
FontSize = 6,
FontFamilyName = "Times New Roman",
DigitalSignedLabel = "Signed by:"
};
signature.CustomAppearance = signatureCustomAppearance;
pdfSign.Sign(1, true, rect, signature);
// 保存输出 PDF 文件
pdfSign.Save(_dataDir + "DigitallySign.pdf");
}
更改数字签名文本中的语言
使用 Aspose.PDF for .NET API，您可以使用以下三种类型的签名之一对 PDF 文件进行签名：
- PKCS#1
- PKCS#7
- PKCS#7
每个提供的签名都包含一组为您的方便而实现的配置属性（本地化、日期时间格式、字体系列等）。类 SignatureCustomAppearance 提供了相应的功能。以下代码片段演示了如何更改数字签名文本中的语言：
public static void ChangeLanguageInDigitalSignText()
{
string inFile = _dataDir + "sample01.pdf";
string outFile = _dataDir + "DigitallySign.pdf";
using (Aspose.Pdf.Facades.PdfFileSignature pdfSign = new Aspose.Pdf.Facades.PdfFileSignature())
{
pdfSign.BindPdf(inFile);
//create a rectangle for signature location
System.Drawing.Rectangle rect = new System.Drawing.Rectangle(310, 45, 200, 50);
//create any of the three signature types
PKCS7 pkcs = new PKCS7(_dataDir + "test01.pfx", "Aspose2021")
{
Reason = "Pruebas Firma",
ContactInfo = "Contacto Pruebas",
Location = "Población (Provincia)",
Date = DateTime.Now
};
SignatureCustomAppearance signatureCustomAppearance = new SignatureCustomAppearance
{
DateSignedAtLabel = "Fecha",
DigitalSignedLabel = "Digitalmente firmado por",
ReasonLabel = "Razón",
LocationLabel = "Localización",
FontFamilyName = "Arial",
FontSize = 10d,
Culture = System.Globalization.CultureInfo.InvariantCulture,
DateTimeFormat = "yyyy.MM.dd HH:mm:ss"
};
pkcs.CustomAppearance = signatureCustomAppearance;
// sign the PDF file
pdfSign.Sign(1, true, rect, pkcs);
//save output PDF file
pdfSign.Save(outFile);
}
}