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A Developer's Guide to Digitally Signing PDFs with C#

Jacob Mellor

Updated:July 28, 2025

Adding a signature to a PDF document is a common requirement in many applications, but "signing" can mean different things. For some, it's about applying a tamper-proof digital signature using a security certificate. For others, it might be stamping a visual, handwritten signature image onto a document or adding an interactive form field for users to sign electronically.

This guide provides a comprehensive walkthrough for C# developers on how to accomplish all of these tasks using the IronPDF for .NET library. We will cover everything from applying a secure X509Certificate2 digital signature to stamping graphical signatures and creating interactive signature fields, ensuring your PDF documents are authentic, secure, and professional.

How to Programmatically Sign a PDF File in C#

1. Install the IronPDF library for .NET.
2. Apply a digital signature using an X509Certificate2 object.
3. Add a visual image to represent the digital signature.
4. Stamp a graphical or handwritten signature onto a PDF file.
5. Add an interactive signature form field for electronic signing.

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First Step:

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How Do I Apply a Digital Signature to a PDF with a Certificate?

You can apply a digital signature to a PDF document using a digital certificate file (such as .pfx or .p12) to guarantee the document's authenticity and integrity. This process ensures that the document has not been altered since it was signed.

IronPDF provides a straightforward API for this purpose, supporting multiple ways to apply a digital signature. The core of this functionality revolves around the PdfSignature class, which encapsulates the certificate and all associated metadata for the signature.

Using an X509Certificate2 Object

For maximum control, you can create an X509Certificate2 object from your certificate file. IronPDF fully complies with the X509Certificate2 standard, providing a robust and secure method for digital signature implementation. When creating the certificate object, ensure the X509KeyStorageFlags are set to Exportable, as this is required by the underlying cryptographic APIs.

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")

The code above first generates a simple PDF. It then loads a .pfx certificate file into an X509Certificate2 object. This object, which represents the digital identity, is passed to the PdfSignature constructor. Finally, the pdf.Sign method applies this signature to the document before saving it. For more information on the X509Certificate2 class, you can refer to the official Microsoft documentation.

Adding Granular Details to a Digital Signature

A digital signature can contain more than just the certificate; you can embed rich metadata to provide context about the signature. This includes the signing location, reason, contact information, and a secure timestamp from a trusted authority.

Adding these details improves the document's audit trail and provides verifiers with valuable information. IronPDF also supports timestamping servers that use modern SHA256 and SHA512 hash algorithms.

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")

You may notice a warning icon in some PDF viewers if the signing certificate is not in the system's trusted store. To get a green checkmark, the certificate must be added to the viewer's trusted identities.

How Can I Add a Visual Representation to a Digital Signature?

While a digital signature is cryptographically embedded in the PDF, it's often useful to have a visual representation on the page. This can be a company logo, a handwritten signature image, or other graphics. IronPDF makes it easy to add an image to a PdfSignature object.

You can load an image from a file or a stream and position it precisely on any page of the PDF. Supported image formats include PNG, JPEG, GIF, BMP, TIFF, and WebP.

using IronPdf.Signing;
using IronSoftware.Drawing;

// This example demonstrates various ways to add a visual image to a PDF signature.

// Create a PdfSignature object.
var signature = new PdfSignature("IronSoftware.pfx", "123456");

// Define the position and size for the signature image on the first page (index 0).
var signatureRectangle = new Rectangle(350, 750, 200, 100);

// Option 1: Set the SignatureImage property directly.
signature.SignatureImage = new PdfSignatureImage("assets/visual-signature.png", 0, signatureRectangle);

// Option 2: Use the LoadSignatureImageFromFile method.
signature.LoadSignatureImageFromFile("assets/visual-signature.png", 0, signatureRectangle);

// Option 3: Load an image from a stream. This is useful for images generated in memory.
AnyBitmap image = AnyBitmap.FromFile("assets/visual-signature.png");
using (var imageStream = image.ToStream())
{
    signature.LoadSignatureImageFromStream(imageStream, 0, signatureRectangle);
}

// After configuring the signature image, apply it to a PDF.
var pdf = PdfDocument.FromFile("invoice.pdf");
pdf.Sign(signature);
pdf.SaveAs("VisualSignature.pdf");
</span><br class="ProseMirror-trailingBreak">

using IronPdf.Signing;
using IronSoftware.Drawing;

// This example demonstrates various ways to add a visual image to a PDF signature.

// Create a PdfSignature object.
var signature = new PdfSignature("IronSoftware.pfx", "123456");

// Define the position and size for the signature image on the first page (index 0).
var signatureRectangle = new Rectangle(350, 750, 200, 100);

// Option 1: Set the SignatureImage property directly.
signature.SignatureImage = new PdfSignatureImage("assets/visual-signature.png", 0, signatureRectangle);

// Option 2: Use the LoadSignatureImageFromFile method.
signature.LoadSignatureImageFromFile("assets/visual-signature.png", 0, signatureRectangle);

// Option 3: Load an image from a stream. This is useful for images generated in memory.
AnyBitmap image = AnyBitmap.FromFile("assets/visual-signature.png");
using (var imageStream = image.ToStream())
{
    signature.LoadSignatureImageFromStream(imageStream, 0, signatureRectangle);
}

// After configuring the signature image, apply it to a PDF.
var pdf = PdfDocument.FromFile("invoice.pdf");
pdf.Sign(signature);
pdf.SaveAs("VisualSignature.pdf");
</span><br class="ProseMirror-trailingBreak">

Imports IronPdf.Signing
Imports IronSoftware.Drawing

' This example demonstrates various ways to add a visual image to a PDF signature.

' Create a PdfSignature object.
Private signature = New PdfSignature("IronSoftware.pfx", "123456")

' Define the position and size for the signature image on the first page (index 0).
Private signatureRectangle = New Rectangle(350, 750, 200, 100)

' Option 1: Set the SignatureImage property directly.
signature.SignatureImage = New PdfSignatureImage("assets/visual-signature.png", 0, signatureRectangle)

' Option 2: Use the LoadSignatureImageFromFile method.
signature.LoadSignatureImageFromFile("assets/visual-signature.png", 0, signatureRectangle)

' Option 3: Load an image from a stream. This is useful for images generated in memory.
Dim image As AnyBitmap = AnyBitmap.FromFile("assets/visual-signature.png")
Using imageStream = image.ToStream()
	signature.LoadSignatureImageFromStream(imageStream, 0, signatureRectangle)
End Using

' After configuring the signature image, apply it to a PDF.
Dim pdf = PdfDocument.FromFile("invoice.pdf")
pdf.Sign(signature)
pdf.SaveAs("VisualSignature.pdf")
'INSTANT VB TODO TASK: The following line uses invalid syntax:
'</span><br class="ProseMirror-trailingBreak">

This code showcases three equivalent ways to add a visual component to a digital signature. Whether you have an image on disk or in memory, you can easily stamp it onto the PDF as part of the signing process. This bridges the gap between invisible cryptographic security and visible document approval.

How Can I Control Document Permissions After Signing?

When you sign a document, you might want to specify what changes, if any, are permitted afterward. For example, you might want to lock the document completely or only allow users to fill in form fields. IronPDF lets you set these permissions using the SignaturePermissions enumeration.

Setting signature permissions is a key part of managing a document's lifecycle. It ensures that the document's integrity is maintained according to your rules after your signature is applied. If a user performs a disallowed action, the signature will be invalidated.

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")

How Do I Stamp a Handwritten Signature onto a PDF?

Sometimes, you don't need the cryptographic security of a digital signature but simply want to apply a visual, electronic signature, like a scanned handwritten signature. This is often referred to as stamping. IronPDF can do this using its Watermark or Stamp features.

Let's start with a sample invoice PDF and a .png image of a handwritten signature.

The original invoice PDF before stamping a signature.

Here is the signature image we will apply:

A sample handwritten signature image.

The following code uses the Watermark property to stamp this image onto the bottom-right corner of the PDF.

using IronPdf.Editing;

// Load the existing PDF document.
var pdf = PdfDocument.FromFile("invoice.pdf");

// Create an HtmlStamp containing our signature image.
var signatureStamp = new HtmlStamp("<img src='assets/signature.png'/>")
{
    // Configure the stamp's position and appearance.
    VerticalAlignment = VerticalAlignment.Bottom,
    HorizontalAlignment = HorizontalAlignment.Right,
    Margin = 10, // Add some space from the edge.
    Opacity = 90 // Make it slightly transparent.
};

// Apply the stamp to all pages of the PDF.
pdf.ApplyStamp(signatureStamp);

// Save the modified PDF document.
pdf.SaveAs("official_invoice.pdf");

using IronPdf.Editing;

// Load the existing PDF document.
var pdf = PdfDocument.FromFile("invoice.pdf");

// Create an HtmlStamp containing our signature image.
var signatureStamp = new HtmlStamp("<img src='assets/signature.png'/>")
{
    // Configure the stamp's position and appearance.
    VerticalAlignment = VerticalAlignment.Bottom,
    HorizontalAlignment = HorizontalAlignment.Right,
    Margin = 10, // Add some space from the edge.
    Opacity = 90 // Make it slightly transparent.
};

// Apply the stamp to all pages of the PDF.
pdf.ApplyStamp(signatureStamp);

// Save the modified PDF document.
pdf.SaveAs("official_invoice.pdf");

Imports IronPdf.Editing

' Load the existing PDF document.
Private pdf = PdfDocument.FromFile("invoice.pdf")

' Create an HtmlStamp containing our signature image.
Dim signatureStamp = New HtmlStamp("<img src='assets/signature.png'/>")
If True Then
	' Configure the stamp's position and appearance.
'INSTANT VB WARNING: An assignment within expression was extracted from the following statement:
'ORIGINAL LINE: VerticalAlignment = VerticalAlignment.Bottom, HorizontalAlignment = HorizontalAlignment.Right, Margin = 10, Opacity = 90
	10, Opacity = 90 ' Make it slightly transparent.
'INSTANT VB WARNING: An assignment within expression was extracted from the following statement:
'ORIGINAL LINE: VerticalAlignment = VerticalAlignment.Bottom, HorizontalAlignment = HorizontalAlignment.Right, Margin = 10, Opacity
	HorizontalAlignment.Right, Margin = 10, Opacity
'INSTANT VB WARNING: An assignment within expression was extracted from the following statement:
'ORIGINAL LINE: VerticalAlignment = VerticalAlignment.Bottom, HorizontalAlignment = HorizontalAlignment.Right, Margin
	VerticalAlignment.Bottom, HorizontalAlignment = HorizontalAlignment.Right, Margin
	VerticalAlignment = VerticalAlignment.Bottom, HorizontalAlignment
End If

' Apply the stamp to all pages of the PDF.
pdf.ApplyStamp(signatureStamp)

' Save the modified PDF document.
pdf.SaveAs("official_invoice.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.

How Can I Add an Interactive Signature Field to a PDF?

For documents that need to be signed by an end-user in a PDF viewer like Adobe Acrobat, you can add an interactive signature form field. This creates an empty, clickable area that prompts the user to apply their own digital signature.

You can create a SignatureFormField and add it to the PDF's form collection. You have precise control over its location and size on the page.

using IronPdf.Forms;
using IronSoftware.Drawing;

// Create a new PDF to add the signature field to.
var renderer = new ChromePdfRenderer();
var pdf = renderer.RenderHtmlAsPdf("<h1>Please Sign Below</h1>");

// Define the properties for the signature form field.
string fieldName = "ClientSignature";
int pageIndex = 0; // Add to the first page.
var fieldRect = new Rectangle(50, 200, 300, 100); // Position: (x, y), Size: (width, height)

// Create the SignatureFormField object.
var signatureField = new SignatureFormField(fieldName, pageIndex, fieldRect);

// Add the signature field to the PDF's form.
pdf.Form.Add(signatureField);

// Save the PDF with the new interactive signature field.
pdf.SaveAs("interactive_signature.pdf");

using IronPdf.Forms;
using IronSoftware.Drawing;

// Create a new PDF to add the signature field to.
var renderer = new ChromePdfRenderer();
var pdf = renderer.RenderHtmlAsPdf("<h1>Please Sign Below</h1>");

// Define the properties for the signature form field.
string fieldName = "ClientSignature";
int pageIndex = 0; // Add to the first page.
var fieldRect = new Rectangle(50, 200, 300, 100); // Position: (x, y), Size: (width, height)

// Create the SignatureFormField object.
var signatureField = new SignatureFormField(fieldName, pageIndex, fieldRect);

// Add the signature field to the PDF's form.
pdf.Form.Add(signatureField);

// Save the PDF with the new interactive signature field.
pdf.SaveAs("interactive_signature.pdf");

Imports IronPdf.Forms
Imports IronSoftware.Drawing

' Create a new PDF to add the signature field to.
Private renderer = New ChromePdfRenderer()
Private pdf = renderer.RenderHtmlAsPdf("<h1>Please Sign Below</h1>")

' Define the properties for the signature form field.
Private fieldName As String = "ClientSignature"
Private pageIndex As Integer = 0 ' Add to the first page.
Private fieldRect = New Rectangle(50, 200, 300, 100) ' Position: (x, y), Size: (width, height)

' Create the SignatureFormField object.
Private signatureField = New SignatureFormField(fieldName, pageIndex, fieldRect)

' Add the signature field to the PDF's form.
pdf.Form.Add(signatureField)

' Save the PDF with the new interactive signature field.
pdf.SaveAs("interactive_signature.pdf")

When a user opens this PDF, they will see a clickable field, allowing them to complete the signing process using their own digital ID. You can learn more about creating and managing interactive forms in our How-To guide on creating PDF forms.

An unsigned, interactive signature field added programmatically to a PDF document.

Next Steps

This guide has demonstrated the powerful and flexible PDF signing capabilities of IronPDF. Whether you need to apply secure digital signatures with detailed metadata, manage document revisions, stamp visual signatures, or create interactive forms, IronPDF provides a comprehensive and developer-friendly API to get the job done.

To continue exploring, you can download the IronPDF library for .NET and get a free trial license to test out all its features in your projects.

Ready to see what else you can do? Check out our tutorial page here: Sign and Secure PDFs

Jacob Mellor

  Chat with engineering team now

Chief Technology Officer

Jacob Mellor is Chief Technology Officer at Iron Software and a visionary engineer pioneering C# PDF technology. As the original developer behind Iron Software's core codebase, he has shaped the company's product architecture since its inception, transforming it alongside CEO Cameron Rimington into a 50+ person company serving NASA, Tesla, and global government agencies.

Jacob holds a First-Class Honours Bachelor of Engineering (BEng) in Civil Engineering from the University of Manchester (1998–2001). After opening his first software business in London in 1999 and creating his first .NET components in 2005, he specialized in solving complex problems across the Microsoft ecosystem.

His flagship IronPDF & IronSuite .NET libraries have achieved over 30 million NuGet installations globally, with his foundational code continuing to power developer tools used worldwide. With 25 years of commercial experience and 41 years of coding expertise, Jacob remains focused on driving innovation in enterprise-grade C#, Java, and Python PDF technologies while mentoring the next generation of technical leaders.

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Jeffrey T. Fritz

Principal Program Manager - .NET Community Team

Jeff is also a Principal Program Manager for the .NET and Visual Studio teams. He is the executive producer of the .NET Conf virtual conference series and hosts 'Fritz and Friends' a live stream for developers that airs twice weekly where he talks tech and writes code together with viewers. Jeff writes workshops, presentations, and plans content for the largest Microsoft developer events including Microsoft Build, Microsoft Ignite, .NET Conf, and the Microsoft MVP Summit

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