• 对PDF文档进行数字签名的需求
• 对PDF文档添加水印的需求
• 网上资料版本不一或不全

本文章提到的Spire.Pdf均是使用的Spire.Pdf for .NET，除此之前还有其他语言的版本，如Spire.Pdf for JAVA；
Spire.Pdf主要用于操作PDF，另外还有Spire.Excel、Spire.Doc等
主要介绍了在C#中使用Spire.Pdf组件包对PDF文档进行数字签名、添加水印功能，旨在引导大家快速、轻松的对PDF文档进行数字签名和添加水印功能；

Spire.PDF for .NET 是一款专业的基于.NET平台的PDF文档控制组件。它能够让开发人员在不使用Adobe Acrobat和其他外部控件的情况下，运用.NET 应用程序创建，阅读，编写和操纵PDF 文档。Spire.PDF for .NET 功能丰富，除了基本的功能比如：绘制多种图形，图片，创建窗体字段，插入页眉页脚，输入数据表，自动对大型表格进行分页外，Spire.PDF for .NET还支持PDF数字签名，将HTML转换成PDF格式，提取PDF文档中的文本信息和图片等，目前Spire.PDF for .NET共有两个版本，一个是免费版本一个是付费版本，免费版本如果只是处理简单的pdf是没问题的，但是如果涉及到输出为pdf则会只显示前10页，第十一页则是预定的购买页介绍，我这里主要是对PDF文档的数字签名和水印，所以不涉及输出pdf；

本文示例代码依赖于Spire.Pdf，可以在项目中使用NuGet程序包引入。

核心代码

1 public class DigitalSignature
2 {
3 ///

4 /// 页顶部红色警告字样覆盖白色图片Base64. 5 ///

6 private const string WatermarkCoverBase64 = "/9j/4AAQSkZJRgABAQEAYABgAAD/2wBDAAMCAgMCAgMDAwMEAwMEBQgFBQQEBQoHBwYIDAoMDAsKCwsNDhIQDQ4RDgsLEBYQERMUFRUVDA8XGBYUGBIUFRT/2wBDAQMEBAUEBQkFBQkUDQsNFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBT/wAARCABHAycDASIAAhEBAxEB/8QAHwAAAQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUFBAQAAAF9AQIDAAQRBRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RFRkdISUpTVFVWV1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/8QAHwEAAwEBAQEBAQEBAQAAAAAAAAECAwQFBgcICQoL/8QAtREAAgECBAQDBAcFBAQAAQJ3AAECAxEEBSExBhJBUQdhcRMiMoEIFEKRobHBCSMzUvAVYnLRChYkNOEl8RcYGRomJygpKjU2Nzg5OkNERUZHSElKU1RVVldYWVpjZGVmZ2hpanN0dXZ3eHl6goOEhYaHiImKkpOUlZaXmJmaoqOkpaanqKmqsrO0tba3uLm6wsPExcbHyMnK0tPU1dbX2Nna4uPk5ebn6Onq8vP09fb3+Pn6/9oADAMBAAIRAxEAPwD9U6KKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooA//Z";
7
8 ///

9 /// 构造函数. 10 ///

11 /// 待签名文件.
12 /// 签名图片.
13 /// 签名证书.
14 /// 签名证书密码.
15 public DigitalSignature(byte[] waitSignFile, byte[] imageSign, byte[] pfx, string pfxPwd)
16 {
17 this.WaitSignFile = waitSignFile;
18 this.ImageSign = imageSign;
19 this.Pfx = pfx;
20 this.PfxPwd = pfxPwd;
21 }
22
23 ///

24 /// 构造函数. 25 ///

26 /// 待签名文件.
27 /// 签名文字.
28 /// 签名右向左宽度.
29 /// 签名低向上高度.
30 /// 签名证书.
31 /// 签名证书密码.
32 public DigitalSignature(byte[] waitSignFile, string charactersSign, float signRightLeftWidth, float signBottomUpHeight, byte[] pfx, string pfxPwd)
33 {
34 this.WaitSignFile = waitSignFile;
35 this.CharactersSign = charactersSign;
36 this.SignRightLeftWidth = signRightLeftWidth;
37 this.SignBottomUpHeight = signBottomUpHeight;
38 this.Pfx = pfx;
39 this.PfxPwd = pfxPwd;
40 }
41
42 ///

43 /// 构造函数. 44 ///

45 /// 待签名文件.
46 /// 签名图片.
47 /// 签名文字.
48 /// 签名证书.
49 /// 签名证书密码.
50 public DigitalSignature(byte[] waitSignFile, byte[] imageSign, string charactersSign, byte[] pfx, string pfxPwd)
51 {
52 this.WaitSignFile = waitSignFile;
53 this.ImageSign = imageSign;
54 this.CharactersSign = charactersSign;
55 this.Pfx = pfx;
56 this.PfxPwd = pfxPwd;
57 }
58
59 ///

60 /// Gets or sets 待签名文件. 61 ///

62 public byte[] WaitSignFile { get; set; }
63
64 ///

65 /// Gets or sets 图签名. 66 ///

67 public byte[] ImageSign { get; set; }
68
69 ///

70 /// Gets or sets 文字签名. 71 ///

72 public string CharactersSign { get; set; }
73
74 ///

75 /// Gets or sets 签名右向左的宽度. 76 ///

77 public float? SignRightLeftWidth { get; set; }
78
79 ///

80 /// Gets or sets 签名顶向上高度. 81 ///

82 public float? SignBottomUpHeight { get; set; }
83
84 ///

85 /// Gets or sets 签名索引页面（不指定默认所有页进行签名）. 86 ///

87 public int? SignIndexPages { get; set; }
88
89 ///

90 /// Gets or sets Pfx证书. 91 ///

92 public byte[] Pfx { get; set; }
93
94 ///

95 /// Gets or sets Pfx证书密码. 96 ///

97 public string PfxPwd { get; set; }
98
99 public Stream Signature()
100 {
101 ///加载PDF文档
102 PdfDocument pdf = new PdfDocument();
103 pdf.LoadFromBytes(this.WaitSignFile);
104
105 if (pdf?.Pages?.Count <= 0) 106 { 107 throw new Exception("文件有误"); 108 } 109 110 X509Certificate2 x509 = new X509Certificate2(this.Pfx, this.PfxPwd); 111 PdfOrdinarySignatureMaker signatureMaker = new PdfOrdinarySignatureMaker(pdf, x509); 112 113 var appearance = new PdfCustomSignatureAppearance(this.CharactersSign, this.ImageSign, this.SignRightLeftWidth, this.SignBottomUpHeight); 114 IPdfSignatureAppearance signatureAppearance = appearance; 115 116 // 绘画白底图片 117 PdfRubberStampAnnotation logoStamp = new PdfRubberStampAnnotation(new RectangleF(new PointF(0, 0), new SizeF(350, 22))); 118 PdfAppearance logoApprearance = new PdfAppearance(logoStamp); 119 //var logoPath = AppDomain.CurrentDomain.BaseDirectory + "\\white.jpg"; 120 byte[] byt = Convert.FromBase64String(WatermarkCoverBase64); 121 Stream streamByLogo = new MemoryStream(byt); 122 PdfImage image = PdfImage.FromStream(streamByLogo); 123 PdfTemplate template = new PdfTemplate(350, 22); 124 template.Graphics.DrawImage(image, 0, 0); 125 logoApprearance.Normal = template; 126 logoStamp.Appearance = logoApprearance; 127 128 if (this.SignIndexPages.HasValue) 129 { 130 if (this.SignIndexPages.Value < 0 || this.SignIndexPages.Value > pdf?.Pages?.Count)
131 {
132 throw new Exception("签名索引页有误");
133 }
134
135 var page = pdf.Pages[this.SignIndexPages.Value];
136
137 // 添加白底图片覆盖页面顶部印记
138 page.AnnotationsWidget.Add(logoStamp);
139
140 // 在页面中的指定位置添加可视化签名
141 signatureMaker.MakeSignature("signName_", page, page.ActualSize.Width - appearance.SignRightLeftWidth, page.ActualSize.Height - appearance.SignBottomUpHeight, appearance.SignRightLeftWidth, appearance.SignBottomUpHeight, signatureAppearance);
142 }
143 else
144 {
145 foreach (PdfPageBase page in pdf.Pages)
146 {
147 // 添加白底图片覆盖页面顶部印记
148 page.AnnotationsWidget.Add(logoStamp);
149
150 // 在页面中的指定位置添加可视化签名
151 signatureMaker.MakeSignature("signName_", page, page.ActualSize.Width - appearance.SignRightLeftWidth, page.ActualSize.Height - appearance.SignBottomUpHeight, appearance.SignRightLeftWidth, appearance.SignBottomUpHeight, signatureAppearance);
152 }
153 }
154
155 MemoryStream stream = new MemoryStream();
156 pdf.SaveToStream(stream, FileFormat.PDF);
157 pdf.Close();
158 return stream;
159 }
160
161 ///

162 /// 使用第三方插件 =》 去除 Evaluation Warning : The document was created with Spire.PDF for .NET. 163 ///

164 /// 原文件地址
165 //private static MemoryStream ClearPdfFilesFirstPage(MemoryStream sourcePdf)
166 //{
167 // iTextSharp.text.pdf.PdfReader reader = null;
168 // iTextSharp.text.Document document = new iTextSharp.text.Document();
169 // iTextSharp.text.pdf.PdfImportedPage page = null;
170 // iTextSharp.text.pdf.PdfCopy pdfCpy = null;
171 // int n = 0;
172 // reader = new iTextSharp.text.pdf.PdfReader(sourcePdf);
173 // reader.ConsolidateNamedDestinations();
174 // n = reader.NumberOfPages;
175 // document = new iTextSharp.text.Document(reader.GetPageSizeWithRotation(1));
176 // MemoryStream memoryStream = new MemoryStream();
177 // pdfCpy = new iTextSharp.text.pdf.PdfCopy(document, memoryStream);
178 // document.Open();
179 // for (int j = 2; j <= n; j++) 180 // { 181 // page = pdfCpy.GetImportedPage(reader, j); 182 // pdfCpy.AddPage(page); 183 184 // } 185 // reader.Close(); 186 // document.Close(); 187 // return memoryStream; 188 //} 189 } 190 191 192 public class PdfCustomSignatureAppearance : IPdfSignatureAppearance 193 { 194 public PdfCustomSignatureAppearance(string charactersSign, byte[] sign, float? signRightLeftWidth, float? signBottomUpHeight) 195 { 196 this.CharactersSign = charactersSign; 197 198 if (sign != null && sign.Length > 0)
199 {
200 this.Sign = sign;
201 MemoryStream ms = new MemoryStream(sign);
202 var image = System.Drawing.Image.FromStream(ms);
203 if (!signRightLeftWidth.HasValue)
204 {
205 signRightLeftWidth = image.Width;
206 }
207
208 if (!signBottomUpHeight.HasValue)
209 {
210 signBottomUpHeight = image.Height;
211 }
212 }
213
214 this.SignRightLeftWidth = signRightLeftWidth.Value;
215 this.SignBottomUpHeight = signBottomUpHeight.Value;
216 }
217
218 ///

219 /// Gets or sets 签名. 220 ///

221 public byte[] Sign { get; set; }
222
223 ///

224 /// Gets or sets 签名右向左的宽度. 225 ///

226 public float SignRightLeftWidth { get; set; }
227
228 ///

229 /// Gets or sets 签名顶向上高度. 230 ///

231 public float SignBottomUpHeight { get; set; }
232
233 ///

234 /// Gets or sets 文字签名. 235 ///

236 public string CharactersSign { get; set; }
237
238 public void Generate(PdfCanvas g)
239 {
240 if (!string.IsNullOrWhiteSpace(CharactersSign))
241 {
242 float fontSize = 15;
243 var font = new System.Drawing.Font("Arial", fontSize);
244 PdfTrueTypeFont fontByPdf = new PdfTrueTypeFont(font, true);
245 g.DrawString(CharactersSign, fontByPdf, PdfBrushes.Black, new PointF(0, 0));
246 }
247
248 if (this.Sign != null && this.Sign.Length > 0)
249 {
250 Stream stream = new MemoryStream(this.Sign);
251 g.DrawImage(Spire.Pdf.Graphics.PdfImage.FromStream(stream), new PointF(20, 20));
252 }
253 }
254 }

调用实现

1 static void Main(string[] args)
2 {
3
4 /*
5 前言：最近有个需求是需要对文档进行数字签名；
6 描述：本示例基于Spire.Pdf组件对PDF进行数字签名，演示了
7 签名证书使用项目
8 CreateSelfSignedCertificateByBouncyCastle(https://github.com/daileass/CreateSelfSignedCertificateByBouncyCastle.git)
9 生成的自签名证书pfx，解决了数字签名后文档头部有警告
10
11 */
12
13 var fileCert = System.Environment.CurrentDirectory + "\\Cert\\";
14 var file = System.Environment.CurrentDirectory + "\\File\\";
15 var filePath = file + "dome.pdf";
16 var newFilePath = file + $"dome_{DateTime.Now.ToString("yyyyMMddHHmmss")}.pdf";
17 var pfxFilePath = fileCert + "edd9386229324d969692dcabf97ac095dpps.fun.pfx";
18 var pfxFilePwd = "ABCD123456";
19 var signFilePath = file + "sign.png";
20
21 // 数字签名
22 var digitalSignature = new DigitalSignature(
23 File2Bytes(filePath),
24 File2Bytes(signFilePath),
25 "Sign Here:",
26 File2Bytes(pfxFilePath),
27 pfxFilePwd
28 );
29 var stream = digitalSignature.Signature();
30
31 // 保存签名后的文件
32 using (var fileStream = File.Create(newFilePath))
33 {
34 stream.Seek(0, SeekOrigin.Begin);
35 stream.CopyTo(fileStream);
36 }
37
38 Console.WriteLine("OK");
39 Console.ReadLine();
40 }
41
42 ///

43 /// 将文件转换为byte数组 44 ///

45 /// 文件地址
46 /// 转换后的byte数组
47 public static byte[] File2Bytes(string path)
48 {
49 if (!System.IO.File.Exists(path))
50 {
51 return new byte[0];
52 }
53
54 FileInfo fi = new FileInfo(path);
55 byte[] buff = new byte[fi.Length];
56
57 FileStream fs = fi.OpenRead();
58 fs.Read(buff, 0, Convert.ToInt32(fs.Length));
59 fs.Close();
60
61 return buff;
62 }

源码下载：https://github.com/daileass/PDFDigitalSignatureBySelfSignedCertificate.git