Aspose.PDF Signature for .NET

Aspose.PDF Signature for .NET enables developers to programmatically apply, validate, and manage digital signatures within PDF documents. With support for multiple certificate formats, signature appearance customization, timestamping, and metadata access, this plugin ensures document authenticity, integrity, and non-repudiation in .NET applications.

Getting Started

Installation and Setup

  1. Install Aspose.PDF from NuGet or download assemblies directly.

    dotnet add package Aspose.PDF

  2. Configure metered licensing at startup (see Metered Licensing ).

Features and Functionalities

Digital Signature Creation

  • Sign using X.509 certificates (PFX, P12), PKCS#7, CMS, or external providers.
  • Support for RSA and ECDSA cryptographic algorithms.
  • Apply detached or enveloped signatures to entire documents or specific fields.

Signature Verification

  • Inspect and validate existing signatures.
  • Verify certificate integrity and detect modifications.
  • Retrieve signature status (valid, invalid, unknown) with reasons.

Certificate Management

  • Load certificates from files, byte arrays, or stores by thumbprint.
  • Handle password-protected keys.
  • Manage certificate chains and trust stores dynamically.

Signature Appearance Customization

  • Add text, logos, seals, or QR codes to signature appearances.
  • Control fonts, colors, alignment, and rotation.
  • Precisely position signatures on fields or coordinates.

Signature Fields and Form Integration

  • Create new signature fields programmatically or use existing AcroForm fields.
  • Support multi-signature workflows.
  • Enforce field properties (required, locked after signing).

Timestamping Support

  • Attach RFC 3161 timestamps from TSA servers.
  • Validate existing timestamps.
  • Configure TSA URL, credentials, and policies.

Signature Audit and Reporting

  • Extract signer details (name, reason, location, contact).
  • Access creation and modification dates.
  • Generate audit logs or compliance reports.

Code Example: Signing PDF Document 

// Define input and output files
var inputPath = Path.Combine(@"C:\Samples\", "sample.pdf");
var certPath = Path.Combine(@"C:\Samples\", "certificate.pfx");
var outputPath = Path.Combine(@"C:\Samples\", "signed.pdf");

// Create signature instance
var signer = new Signature();

// Configure signature options
var options = new SignOptions
{
    CertificateFile = certPath,
    CertificatePassword = "password",
    Reason = "Document Approval",
    Location = "Head Office",
    Contact = "info@example.com"
};

// Add input and output
options.AddInput(new FileDataSource(inputPath));
options.AddOutput(new FileDataSource(outputPath));

// Process signing
var resultContainer = signer.Process(options);

// Retrieve result
var result = resultContainer.ResultCollection[0];
Console.WriteLine($"Signed PDF saved: {result}");

Tips and Best Practices

  • Always verify certificate chains and trust anchors before signing.
  • Reuse certificate instances in high-volume workflows to reduce I/O.
  • Pre-design signature appearance templates for consistency.
  • Combine timestamping with detached signatures for long-term validity.
  • Lock or flatten fields after signing to prevent unauthorized edits.
  • Log verification results with error reasons for audit trails.

Frequently Asked Questions

What is Aspose.PDF Signature for .NET used for? It allows signing, validating, and managing digital signatures in PDF files within .NET applications.

Which certificate formats are supported? It supports X.509 (PFX, P12), PKCS#7, CMS, and external signature providers.

Can I customize the appearance of digital signatures? Yes, you can add text, images, QR codes, and define fonts, colors, and placement.

Does it support timestamping? Yes, RFC 3161 timestamping is supported via TSA servers.

Can multiple signatures be applied to a document? Yes, it supports multi-signature workflows using AcroForm fields.