使用 C# 對 PDF 進行數位簽章的開發人員指南

使用 X509Certificate2 物件

為了獲得最大程度的控制，您可以從憑證檔案建立X509Certificate2物件。 IronPDF 完全符合X509Certificate2標準，為數位簽章實作提供了強大且安全的方法。 在建立證書物件時，請確保將 X509KeyStorageFlags 設定為 Exportable，因為這是底層加密 API 所要求的。在我們的代碼倉庫中查看實用的 數位簽章範例。

Install-Package IronPdf

using IronPdf;
using IronPdf.Signing;
using System.Security.Cryptography.X509Certificates;

// Create a new PDF from an HTML string for demonstration.
var renderer = new ChromePdfRenderer();
var pdf = renderer.RenderHtmlAsPdf("<h1>Signed Document</h1><p>This document has been digitally signed.</p>");

// Load the certificate from a .pfx file with its password.
// The X509KeyStorageFlags.Exportable flag is crucial for allowing the private key to be used in the signing process.
var cert = new X509Certificate2("IronSoftware.pfx", "123456", X509KeyStorageFlags.Exportable);

// Create a PdfSignature object using the loaded certificate.
var signature = new PdfSignature(cert);

// Apply the signature to the PDF document.
pdf.Sign(signature);

// Save the securely signed PDF document.
pdf.SaveAs("Signed.pdf");

using IronPdf;
using IronPdf.Signing;
using System.Security.Cryptography.X509Certificates;

// Create a new PDF from an HTML string for demonstration.
var renderer = new ChromePdfRenderer();
var pdf = renderer.RenderHtmlAsPdf("<h1>Signed Document</h1><p>This document has been digitally signed.</p>");

// Load the certificate from a .pfx file with its password.
// The X509KeyStorageFlags.Exportable flag is crucial for allowing the private key to be used in the signing process.
var cert = new X509Certificate2("IronSoftware.pfx", "123456", X509KeyStorageFlags.Exportable);

// Create a PdfSignature object using the loaded certificate.
var signature = new PdfSignature(cert);

// Apply the signature to the PDF document.
pdf.Sign(signature);

// Save the securely signed PDF document.
pdf.SaveAs("Signed.pdf");

上面的程式碼首先產生一個簡單的PDF檔案。 然後它將.pfx憑證檔案載入到X509Certificate2物件中。 此物件代表數位身份，並傳遞給PdfSignature建構函數。 最後， pdf.Sign方法會在儲存文件之前將此簽章套用到文件上。 For more information on the X509Certificate2 class, you can refer to the official Microsoft documentation.

為數位簽名添加詳細信息

數位簽章可以包含憑證以外的內容； 您可以嵌入豐富的元數據，以提供有關簽名的上下文資訊。 這包括簽署地點、原因、聯絡資訊以及來自可信任機構的安全時間戳。 您也可以設定和編輯元資料，以取得額外的文件屬性。

添加這些細節可以改進文件的審計跟踪，並為核實人員提供有價值的資訊。 IronPDF 也支援使用現代SHA256和SHA512雜湊演算法的時間戳伺服器。

using IronPdf;
using IronPdf.Signing;
using IronSoftware.Drawing;
using System;

// Load an existing PDF document to be signed.
var pdf = PdfDocument.FromFile("invoice.pdf");

// Create a PdfSignature object directly from the certificate file and password.
var signature = new PdfSignature("IronSoftware.pfx", "123456");

// Add detailed metadata to the signature for a comprehensive audit trail.
// These properties enhance the signature's credibility and provide context
signature.SignatureDate = DateTime.Now;
signature.SigningContact = "legal@ironsoftware.com";
signature.SigningLocation = "Chicago, USA";
signature.SigningReason = "Contractual Agreement";

// Add a secure timestamp from a trusted Time Stamp Authority (TSA).
// This provides cryptographic proof of the signing time.
signature.TimeStampUrl = new Uri("[http://timestamp.digicert.com](http://timestamp.digicert.com)");
signature.TimestampHashAlgorithm = TimestampHashAlgorithms.SHA256;

// Apply a visual appearance to the signature. (More on this in the next section)
signature.SignatureImage = new PdfSignatureImage("assets/visual-signature.png", 0, new Rectangle(350, 750, 200, 100));

// Sign the PDF document with the configured signature object.
pdf.Sign(signature);

// Save the final, signed PDF document.
pdf.SaveAs("DetailedSignature.pdf");

using IronPdf;
using IronPdf.Signing;
using IronSoftware.Drawing;
using System;

// Load an existing PDF document to be signed.
var pdf = PdfDocument.FromFile("invoice.pdf");

// Create a PdfSignature object directly from the certificate file and password.
var signature = new PdfSignature("IronSoftware.pfx", "123456");

// Add detailed metadata to the signature for a comprehensive audit trail.
// These properties enhance the signature's credibility and provide context
signature.SignatureDate = DateTime.Now;
signature.SigningContact = "legal@ironsoftware.com";
signature.SigningLocation = "Chicago, USA";
signature.SigningReason = "Contractual Agreement";

// Add a secure timestamp from a trusted Time Stamp Authority (TSA).
// This provides cryptographic proof of the signing time.
signature.TimeStampUrl = new Uri("[http://timestamp.digicert.com](http://timestamp.digicert.com)");
signature.TimestampHashAlgorithm = TimestampHashAlgorithms.SHA256;

// Apply a visual appearance to the signature. (More on this in the next section)
signature.SignatureImage = new PdfSignatureImage("assets/visual-signature.png", 0, new Rectangle(350, 750, 200, 100));

// Sign the PDF document with the configured signature object.
pdf.Sign(signature);

// Save the final, signed PDF document.
pdf.SaveAs("DetailedSignature.pdf");

如果簽章憑證不在系統的受信任儲存區中，您可能會在某些 PDF 檢視器中看到警告圖示。 要獲得綠色對勾，必須將憑證新增至查看者的受信任身分。

Saving and Signing a Specific PDF Revision

PDFs can store a history of changes, much like a version control system. This is known as incremental saving. When you sign a PDF, the signature applies to a specific revision of the document. This is crucial for workflows where a document goes through multiple stages of approval. Learn more about managing PDF revision history in our detailed guide.

In the following example, we load a PDF, make edits, and then sign the current revision while allowing only form-filling as a future change. We use SaveAsRevision to commit the current state to the document's history before saving the file.

using IronPdf.Signing;

// Load a PDF file with change tracking enabled.
// This enables incremental save functionality for revision management
var pdf = PdfDocument.FromFile("annual_census.pdf", ChangeTrackingModes.EnableChangeTracking);

// Placeholder for edits: You might add text, fill forms, or add annotations here.
// For example: pdf.Annotations.Add(new TextAnnotation(...));
// Or: pdf.Form["fieldName"].Value = "New Value";

// Sign the current state of the document using SignWithFile for convenience.
// We set permissions to allow further signatures and form filling.
pdf.SignWithFile(
    "assets/IronSignature.p12", 
    "password", 
    SignaturePermissions.AdditionalSignaturesAndFormFillingAllowed);

// Save the current state as a distinct revision within the PDF's history.
// This creates a snapshot that can be referenced later
PdfDocument pdfWithRevision = pdf.SaveAsRevision();

// Save the final PDF with its full revision history to a new file.
pdfWithRevision.SaveAs("annual_census_signed.pdf");

using IronPdf.Signing;

// Load a PDF file with change tracking enabled.
// This enables incremental save functionality for revision management
var pdf = PdfDocument.FromFile("annual_census.pdf", ChangeTrackingModes.EnableChangeTracking);

// Placeholder for edits: You might add text, fill forms, or add annotations here.
// For example: pdf.Annotations.Add(new TextAnnotation(...));
// Or: pdf.Form["fieldName"].Value = "New Value";

// Sign the current state of the document using SignWithFile for convenience.
// We set permissions to allow further signatures and form filling.
pdf.SignWithFile(
    "assets/IronSignature.p12", 
    "password", 
    SignaturePermissions.AdditionalSignaturesAndFormFillingAllowed);

// Save the current state as a distinct revision within the PDF's history.
// This creates a snapshot that can be referenced later
PdfDocument pdfWithRevision = pdf.SaveAsRevision();

// Save the final PDF with its full revision history to a new file.
pdfWithRevision.SaveAs("annual_census_signed.pdf");

Understanding incremental saves is key to advanced PDF workflows. While a simple viewer might only show the latest version, a tool like Adobe Acrobat can reveal the entire revision history, showing who signed which version and what changes were made between signatures. IronPDF gives you full programmatic control over this process.

For businesses managing complex document workflows that require high security and compliance, a comprehensive solution may be needed. Iron Software offers Iron Suite, which includes IronPDF for signing and manipulation, plus other libraries for a wide range of document processing tasks, available for a single one-time payment.

How Can I Manage and Verify Signatures Across Revisions?

A PDF document can have multiple signatures applied across its various revisions. IronPDF provides tools to manage this history effectively.

• Roll Back to a Previous Revision: You can revert a document to an earlier state using the GetRevision method. This will discard all changes and signatures made after that revision.
• Verify All Signatures: The VerifySignatures method checks the validity of all signatures across all revisions of the document. It returns true only if every signature is valid and no unauthorized changes have been made.
• Remove Signatures: The RemoveSignatures method will strip all digital signatures from every revision of the document, creating a clean, unsigned version.

// Load a PDF with a complex signature history.
var pdf = PdfDocument.FromFile("multi_signed_report.pdf");

// Verify all signatures across all revisions.
// This ensures document integrity throughout its entire history
bool allSignaturesValid = pdf.VerifySignatures();
Console.WriteLine($"All signatures are valid: {allSignaturesValid}");

// Roll back to the first revision (index 0).
// Useful for reviewing the original document state
if (pdf.RevisionCount > 1)
{
    PdfDocument firstRevision = pdf.GetRevision(0);
    firstRevision.SaveAs("report_first_revision.pdf");
}

// Create a completely unsigned version of the document.
// This removes all digital signatures while preserving content
pdf.RemoveSignatures();
pdf.SaveAs("report_unsigned.pdf");

// Load a PDF with a complex signature history.
var pdf = PdfDocument.FromFile("multi_signed_report.pdf");

// Verify all signatures across all revisions.
// This ensures document integrity throughout its entire history
bool allSignaturesValid = pdf.VerifySignatures();
Console.WriteLine($"All signatures are valid: {allSignaturesValid}");

// Roll back to the first revision (index 0).
// Useful for reviewing the original document state
if (pdf.RevisionCount > 1)
{
    PdfDocument firstRevision = pdf.GetRevision(0);
    firstRevision.SaveAs("report_first_revision.pdf");
}

// Create a completely unsigned version of the document.
// This removes all digital signatures while preserving content
pdf.RemoveSignatures();
pdf.SaveAs("report_unsigned.pdf");

What Does the Stamped PDF Result Look Like?

After running the code, the signature image is stamped onto the document, creating a visually signed invoice.

The final PDF with the handwritten signature image stamped in the bottom-right corner.