Sign PDF Programmatically in C# .NET 10: 디지털 서명 Guide

using IronPdf;
using IronPdf.Signing;

// Load the PDF document that needs to be signed
PdfDocument pdf = PdfDocument.FromFile("contract.pdf");

// Create a signature object using the certificate file path and password
var signature = new PdfSignature("certificate.pfx", "password");

// Apply the cryptographic signature to the document
// This embeds an invisible digital signature in the PDF structure
pdf.Sign(signature);

// Save the signed document to a new file
pdf.SaveAs("contract-signed.pdf");

using IronPdf;
using IronPdf.Signing;

// One-line approach for signing PDFs
// Useful for batch processing where you don't need to manipulate the document
var signature = new PdfSignature("certificate.pfx", "password");
PdfDocument.FromFile("document.pdf").Sign(signature).SaveAs("document-signed.pdf");

using IronPdf;
using IronPdf.Signing;
using System;

// Load the document to be signed
PdfDocument pdf = PdfDocument.FromFile("invoice.pdf");

// Create a signature with the company certificate
var signature = new PdfSignature("certificate.pfx", "password")
{
    // Add metadata to create an audit trail
    // This information appears in the signature panel of PDF readers
    SigningReason = "Invoice Approval",
    SigningLocation = "New York Office",
    SigningContact = "accounts@company.com",
    SignatureDate = DateTime.UtcNow
};

// Apply the signature with all metadata included
pdf.Sign(signature);
pdf.SaveAs("invoice-approved.pdf");

using IronPdf;
using IronPdf.Signing;
using System;

// Load the document to sign
PdfDocument pdf = PdfDocument.FromFile("agreement.pdf");
var signature = new PdfSignature("certificate.pfx", "password")
{
    SigningReason = "Agreement Execution",
    // Configure a trusted timestamp server (RFC 3161 compliant)
    // This provides cryptographic proof of when the document was signed
    TimestampHashAlgorithm = TimestampHashAlgorithms.SHA256,
    TimeStampUrl = "http://timestamp.digicert.com"
};

// Apply the signature with the trusted timestamp
pdf.Sign(signature);
pdf.SaveAs("agreement-timestamped.pdf");

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

// Load the document to sign
PdfDocument pdf = PdfDocument.FromFile("contract.pdf");
var signature = new PdfSignature("certificate.pfx", "password")
{
    SigningReason = "Contract Approval",
    SigningLocation = "Head Office"
};

// Define the position and size for the visible signature image
// Rectangle parameters: x position, y position, width, height (in points)
// Points are measured from the bottom-left corner of the page
var signatureArea = new Rectangle(150, 100, 200, 50);

// Load and attach the visual signature image
// The image will appear at the specified location on the document
signature.LoadSignatureImageFromFile(
    "signature-image.png",   // Path to the signature image file
    0,                       // Page index (0 = first page)
    signatureArea            // Position and dimensions
);

// Apply both the cryptographic signature and visual representation
pdf.Sign(signature);
pdf.SaveAs("contract-visually-signed.pdf");

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

// Create signature object
var signature = new PdfSignature("certificate.pfx", "password");
var signatureArea = new Rectangle(400, 50, 150, 75);

// Method 1: Load signature image directly from a file path
signature.LoadSignatureImageFromFile("signature.png", 0, signatureArea);

// Method 2: Load from a stream (useful for database-stored images)
using (FileStream imageStream = File.OpenRead("signature.png"))
{
    signature.LoadSignatureImageFromStream(imageStream, 0, signatureArea);
}

// Method 3: Load from AnyBitmap (IronSoftware's cross-platform image type)
AnyBitmap signatureBitmap = AnyBitmap.FromFile("signature.png");
using (var stream = signatureBitmap.ToStream())
{
    signature.LoadSignatureImageFromStream(stream, 0, signatureArea);
}

using IronPdf;
using IronPdf.Signing;

// Load a multi-page document
PdfDocument pdf = PdfDocument.FromFile("multi-page-contract.pdf");

// Create signature - digital signatures protect the entire document
// regardless of page count
var signature = new PdfSignature("certificate.pfx", "password");

// Sign and save the document
// The signature applies to all pages in the document
pdf.Sign(signature);
pdf.SaveAs("contract-signed-last-page.pdf");

using IronPdf;
using IronPdf.Editing;
using IronPdf.Signing;
using IronSoftware.Drawing;

// Load the document
PdfDocument pdf = PdfDocument.FromFile("agreement.pdf");

// Create an image stamp for initials that will appear on every page
var initialsStamp = new ImageStamper("initials.png")
{
    HorizontalAlignment = HorizontalAlignment.Right,
    VerticalAlignment = VerticalAlignment.Bottom,
    HorizontalOffset = new Length(50, MeasurementUnit.Points),
    VerticalOffset = new Length(50, MeasurementUnit.Points)
};

// Apply initials stamp to all pages
pdf.ApplyStamp(initialsStamp);

// Now apply the cryptographic signature with a full signature image on the last page
var signature = new PdfSignature("certificate.pfx", "password");
var signatureArea = new Rectangle(100, 100, 200, 100);
signature.SignatureImage = new PdfSignatureImage(
    "full-signature.png",
    pdf.PageCount - 1,    // Last page only
    signatureArea
);

// Sign the entire document cryptographically
pdf.Sign(signature);
pdf.SaveAs("agreement-initialed-and-signed.pdf");

using IronPdf;
using IronPdf.Signing;

// Load the purchase order document
PdfDocument pdf = PdfDocument.FromFile("purchase-order.pdf");

// First signer: Department Manager approves the purchase order
var managerSignature = new PdfSignature("certificate.pfx", "password")
{
    SigningReason = "Manager Approval",
    SigningLocation = "Department A"
};

// Sign the document and save
// This preserves the original state while adding the signature
pdf.Sign(managerSignature);
pdf.SaveAs("po-manager-approved.pdf");

using IronPdf;
using IronPdf.Signing;

// Load the document that already has the manager's signature
PdfDocument pdf = PdfDocument.FromFile("po-manager-approved.pdf");

// Second signer: Finance department verifies budget availability
var financeSignature = new PdfSignature("certificate.pfx", "password")
{
    SigningReason = "Finance Approval",
    SigningLocation = "Finance Department"
};

// Add the second signature
// Both signatures remain independently verifiable
pdf.Sign(financeSignature);
pdf.SaveAs("po-finance-approved.pdf");

using IronPdf;
using IronPdf.Signing;
using System;

// Load the compliance document
PdfDocument pdf = PdfDocument.FromFile("compliance-document.pdf");
var signature = new PdfSignature("certificate.pfx", "password")
{
    // Add comprehensive metadata for audit trail requirements
    SigningReason = "21 CFR Part 11 Compliance Certification",
    SigningLocation = "Quality Assurance Department",
    SigningContact = "compliance@company.com",
    SignatureDate = DateTime.UtcNow,
    // Configure a trusted timestamp for regulatory compliance
    // The timestamp proves when the signature was applied
    TimestampHashAlgorithm = TimestampHashAlgorithms.SHA256,
    TimeStampUrl = "http://timestamp.digicert.com"
};

// Apply the signature with timestamp and full metadata
pdf.Sign(signature);
pdf.SaveAs("compliance-document-certified.pdf");