C#结合Free Spire.PDF实现删除PDF中的数字签名

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

namespace RemoveSignature
{
    class Program
    {
        static void Main(string[] args)
        {
            // 加载要处理的PDF文件
            PdfDocument pdf = new PdfDocument("C:\\Users\\Administrator\\Desktop\\Signature.pdf");

            // 获取文档中的表单域集合
            PdfFormWidget widgets = pdf.Form as PdfFormWidget;

            // 倒序遍历（防止删除时索引错位）
            for (int i = widgets.FieldsWidget.List.Count - 1; i >= 0; i--)
            {
                PdfFieldWidget widget = widgets.FieldsWidget.List[i] as PdfFieldWidget;

                // 判断当前字段是不是数字签名字段
                if (widget is PdfSignatureFieldWidget)
                {
                  // 移除签名
                    widgets.FieldsWidget.RemoveAt(i);
                    Console.WriteLine($"已移除第{i}个签名字段");
                }
            }

            // 保存结果
            pdf.SaveToFile("RemoveSignatures.pdf");
            Console.WriteLine("处理完成！");
            
            // 记得释放资源
            pdf.Close();
        }
    }
}

Install-Package FreeSpire.PDF

using Spire.Pdf;
using Spire.Pdf.Widget;
namespace 移除PDF数字签名
{
    class Program
    {
        static void Main(string[] args)
        {
            PdfDocument pdf = newPdfDocument();
           pdf.LoadFromFile("测试.pdf");
            PdfFormWidget widgets = pdf.Form as PdfFormWidget;
            for (int i = 0; i< widgets.FieldsWidget.List.Count; i++)
            {
               PdfFieldWidget widget =widgets.FieldsWidget.List[i] as PdfFieldWidget;
               if (widget isPdfSignatureFieldWidget)
               {
                   widgets.FieldsWidget.RemoveAt(i);
               }
            }
           pdf.SaveToFile("移除签名.pdf");
           System.Diagnostics.Process.Start("移除签名.pdf");
        }
    }
}

using System.Drawing;
using Spire.Pdf;
using Spire.Pdf.Graphics;
using Spire.Pdf.Security;
namespace Digitally_Sign_Pdf_with_Timestamp
{
    class Program
    {
        static void Main(string[] args)
        {
            //加载PDF文档
            PdfDocument pdf = new PdfDocument();
            pdf.LoadFromFile("Additional.pdf");
            //获取第一页
            PdfPageBase page = pdf.Pages[0];
            //加载数字证书（.pfx文件）
            PdfCertificate cert = new PdfCertificate("test.pfx", "123");
            //加载一张图片
            Spire.Pdf.Graphics.PdfImage image = Spire.Pdf.Graphics.PdfImage.FromFile("Logo.jpg");
            //添加跟图片一样大小的签名到第一页，并设置图片为签名图片
            Spire.Pdf.Security.PdfSignature signature = new Spire.Pdf.Security.PdfSignature(page.Document, page, cert, "sign1");
            signature.Bounds = new RectangleF(new PointF(100, 300), new SizeF(image.Width, image.Height));
            signature.SignImageSource = image;
            signature.GraphicsMode = Spire.Pdf.Security.GraphicMode.SignImageAndSignDetail;
            signature.SignImageLayout = Spire.Pdf.Security.SignImageLayout.Stretch;
            signature.DocumentPermissions = Spire.Pdf.Security.PdfCertificationFlags.AllowFormFill | Spire.Pdf.Security.PdfCertificationFlags.AllowComments;
            //配置时间戳服务器
            string url = "http://timestamp.wosign.com/rfc3161";
            signature.ConfigureTimestamp(url);
            //保存文档
            pdf.SaveToFile("output.pdf");
        }
    }
}