Ein Leitfaden für Entwickler zum digitalen Signieren von PDFs mit C#

Verwendung eines X509Certificate2-Objekts

Für maximale Kontrolle können Sie ein X509Certificate2-Objekt aus Ihrer Zertifikatsdatei erstellen. IronPDF entspricht vollständig dem X509Certificate2-Standard und bietet eine robuste und sichere Methode für die Implementierung digitaler Signaturen. Beim Erstellen des Zertifikatsobjekts muss darauf geachtet werden, dass die X509KeyStorageFlags auf Exportable gesetzt sind, da dies von den zugrunde liegenden kryptografischen APIs erforderlich ist.

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");

Imports IronPdf
Imports IronPdf.Signing
Imports System.Security.Cryptography.X509Certificates

' Create a new PDF from an HTML string for demonstration.
Private renderer = New ChromePdfRenderer()
Private 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.
Private cert = New X509Certificate2("IronSoftware.pfx", "123456", X509KeyStorageFlags.Exportable)

' Create a PdfSignature object using the loaded certificate.
Private signature = New PdfSignature(cert)

' Apply the signature to the PDF document.
pdf.Sign(signature)

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

Der oben stehende Code generiert zuerst ein einfaches PDF. Anschließend wird eine .pfx-Zertifikatsdatei in ein X509Certificate2-Objekt geladen. Dieses Objekt, das die digitale Identität darstellt, wird an den PdfSignature-Konstruktor übergeben. Schließlich wendet die pdf.Sign-Methode diese Signatur auf das Dokument an, bevor es gespeichert wird. For more information on the X509Certificate2 class, you can refer to the official Microsoft documentation.

Zusätzliche Details zu einer digitalen Signatur hinzufügen

Eine digitale Signatur kann mehr als nur das Zertifikat enthalten; Sie können reichhaltige Metadaten einbetten, um Kontext zur Signatur bereitzustellen. Dazu gehören der Ort der Signatur, der Grund, die Kontaktinformationen und ein sicherer Zeitstempel von einer vertrauenswürdigen Behörde.

Das Hinzufügen dieser Details verbessert die Prüfspur des Dokuments und liefert Prüfern wertvolle Informationen. IronPDF unterstützt auch Zeitstempelserver, die moderne SHA256 und SHA512 Hash-Algorithmen verwenden.

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.
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.
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");

Imports IronPdf
Imports IronPdf.Signing
Imports IronSoftware.Drawing
Imports System

' Load an existing PDF document to be signed.
Private pdf = PdfDocument.FromFile("invoice.pdf")

' Create a PdfSignature object directly from the certificate file and password.
Private signature = New PdfSignature("IronSoftware.pfx", "123456")

' Add detailed metadata to the signature for a comprehensive audit trail.
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")

Sie bemerken möglicherweise ein Warnsymbol in einigen PDF-Viewern, wenn das Signaturzertifikat nicht im vertrauenswürdigen Speicher des Systems vorhanden ist. Um ein grünes Häkchen zu bekommen, muss das Zertifikat zu den vertrauenswürdigen Identitäten des Viewers hinzugefügt werden.

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.

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.
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(...));

// 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.
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.
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(...));

// 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.
PdfDocument pdfWithRevision = pdf.SaveAsRevision();

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

Imports IronPdf.Signing

' Load a PDF file with change tracking enabled.
Private 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(...));

' 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.
Dim pdfWithRevision As PdfDocument = 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.
bool allSignaturesValid = pdf.VerifySignatures();
Console.WriteLine($"All signatures are valid: {allSignaturesValid}");

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

// Create a completely unsigned version of the document.
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.
bool allSignaturesValid = pdf.VerifySignatures();
Console.WriteLine($"All signatures are valid: {allSignaturesValid}");

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

// Create a completely unsigned version of the document.
pdf.RemoveSignatures();
pdf.SaveAs("report_unsigned.pdf");

' Load a PDF with a complex signature history.
Dim pdf = PdfDocument.FromFile("multi_signed_report.pdf")

' Verify all signatures across all revisions.
Dim allSignaturesValid As Boolean = pdf.VerifySignatures()
Console.WriteLine($"All signatures are valid: {allSignaturesValid}")

' Roll back to the first revision (index 0).
If pdf.RevisionCount And gt; 1 Then
	Dim firstRevision As PdfDocument = pdf.GetRevision(0)
	firstRevision.SaveAs("report_first_revision.pdf")
End If

' Create a completely unsigned version of the document.
pdf.RemoveSignatures()
pdf.SaveAs("report_unsigned.pdf")

Stamped PDF Result

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.