C# 获取PDF中的数字签名证书

using Spire.Pdf;
using Spire.Pdf.Widget;
using System;

namespace GetCertificateInfo
{
    class Program
    {
        static void Main(string[] args)
        {
            //实例化PdfDocument类的对象，并加载PDF文档
            PdfDocument pdf = new PdfDocument();
            pdf.LoadFromFile("test.pdf");

            //获取域集合
            PdfFormWidget pdfFormWidget = (PdfFormWidget)pdf.Form;
            PdfFormFieldWidgetCollection pdfFormFieldWidgetCollection = pdfFormWidget.FieldsWidget;

            //遍历域
            for (int i = 0; i < pdfFormFieldWidgetCollection.Count; i++)
            {
                //判定是否为签名域
                if (pdfFormFieldWidgetCollection[i] is PdfSignatureFieldWidget)
                {
                    //获取签名域
                    PdfSignatureFieldWidget signatureFieldWidget = (PdfSignatureFieldWidget)pdfFormFieldWidgetCollection[i];

                    //获取签名证书
                    string certificateInfo = signatureFieldWidget.Signature.Certificate.ToString();
                    
                    //获取证书格式
                    string format = signatureFieldWidget.Signature.Certificate.GetFormat();

                    Console.WriteLine(certificateInfo+ "\n"+ "[CertificateFormat]\n " + format );
                }
            }
            Console.ReadKey();          
        }
    }
}

Imports Spire.Pdf
Imports Spire.Pdf.Widget

Namespace GetCertificateInfo
    Class Program
        Private Shared Sub Main(args As String())
            '实例化PdfDocument类的对象，并加载PDF文档
            Dim pdf As New PdfDocument()
            pdf.LoadFromFile("test.pdf")

            '获取域集合
            Dim pdfFormWidget As PdfFormWidget = DirectCast(pdf.Form, PdfFormWidget)
            Dim pdfFormFieldWidgetCollection As PdfFormFieldWidgetCollection = pdfFormWidget.FieldsWidget

            '遍历域
            For i As Integer = 0 To pdfFormFieldWidgetCollection.Count - 1
                '判定是否为签名域
                If TypeOf pdfFormFieldWidgetCollection(i) Is PdfSignatureFieldWidget Then
                    '获取签名域
                    Dim signatureFieldWidget As PdfSignatureFieldWidget = DirectCast(pdfFormFieldWidgetCollection(i), PdfSignatureFieldWidget)

                    '获取签名证书
                    Dim certificateInfo As String = signatureFieldWidget.Signature.Certificate.ToString()

                    '获取证书格式
                    Dim format As String = signatureFieldWidget.Signature.Certificate.GetFormat()

                    Console.WriteLine(Convert.ToString((certificateInfo & Convert.ToString(vbLf)) + "[CertificateFormat]" & vbLf & " ") & format)
                End If
            Next
            Console.ReadKey()
        End Sub
    End Class
End Namespace