Among the various formats used for document exchange, the Portable Document Format (PDF) has become the gold standard due to its consistency and cross-platform compatibility. However, as digital workflows grow, so do concerns about document authenticity, security and trust. PDF document signing addresses these concerns and provides a number of benefits that organizations and individuals cannot afford to overlook.

One of the most important reasons to sign a PDF is to ensure the security of the document. A digitally signed PDF is a document that has been signed using cryptographic technology to verify that the document has not been altered since the signing. This protects against tampering and ensures the integrity of the document's contents.

When you open a signed PDF document in Acrobat Reader, you see the signatures in the Signatures sidebar, and Acrobat also notifies the user by displaying an information bar at the top.

PDF signed with TX Text Control

Digital signatures often rely on Public Key Infrastructure (PKI), which uses a pair of keys-a private key for signing and a public key for verifying. This mechanism provides robust protection against unauthorized changes and ensures that the recipient can trust the authenticity of the document.

Building Trust

A signed PDF builds trust between parties. Whether you are sending a contract, invoice, or official communication, a signature communicates that the document is authentic and that you stand behind its contents. For organizations, this builds credibility with customers, partners, and stakeholders. In addition, digital signatures can include additional verification details, such as timestamps and the signer's identity, adding another layer of trust. These elements assure recipients that the document is not only authentic, but was signed by the intended party at a specific time.

In business, first impressions count. A signed document reflects a level of professionalism and attention to detail that underscores your commitment to quality and integrity. It shows that you are serious about protecting sensitive information and adhering to document management best practices. Unsigned PDFs, on the other hand, can raise questions about their legitimacy, potentially leading to delays or a lack of confidence in the transaction. By signing your documents, you streamline processes and ensure smoother communication.

Many industries are subject to strict legal and regulatory requirements. Digital signatures are often a necessity for compliance with standards such as the General Data Protection Regulation (GDPR) in Europe, the Electronic Signatures in Global and National Commerce Act (ESIGN) in the United States, and the eIDAS regulation for electronic identification in the EU.

Failure to sign critical documents can expose organizations to legal risks and penalties. A signed PDF serves as legally binding proof of agreement or acknowledgment, reducing potential liability and disputes.

Creating the Application

To demonstrate how easy this is with the TX Text Control library, we will use a .NET console application.

Make sure that you downloaded the latest version of Visual Studio 2022 that comes with the .NET 8 SDK.

Prerequisites

The following tutorial requires a trial version of TX Text Control .NET Server for ASP.NET.

  1. In Visual Studio 2022, create a new project by choosing Create a new project.

  2. Select Console App as the project template and confirm with Next.

  3. Choose a name for your project and confirm with Next.

  4. In the next dialog, choose .NET 8 (Long-term support) as the Framework and confirm with Create.

Adding the NuGet Package

  1. In the Solution Explorer, select your created project and choose Manage NuGet Packages... from the Project main menu.

    Select Text Control Offline Packages from the Package source drop-down.

    Install the latest versions of the following package:

    • TXTextControl.TextControl.ASP.SDK

    ASP.NET Core Web Application

Signing a Document

Assuming you have a PFX file locally in your application, add the following code to Program.cs.

using System.Security.Cryptography.X509Certificates;
using TXTextControl;
// Define the certificate password and path
const string password = "123";
const string certificatePath = "certificate.pfx";
var cert = new X509Certificate2(certificatePath, password);
// Initialize TXTextControl to create and save a document with the digital signature
using (var tx = new ServerTextControl())
{
tx.Create();
tx.Text = "Hello, World!";
// Prepare the digital signature for the document
var saveSettings = new SaveSettings
{
DigitalSignature = new DigitalSignature(cert, null)
};
// Save the document as a PDF with the digital signature
tx.Save("result.pdf", StreamType.AdobePDF, saveSettings);
}
view raw test.cs hosted with ❤ by GitHub

This code creates a new document and saves the file as a PDF, encrypted and signed with the given PFX certificate.

Learn More

This article shows how to sign PDF documents with PFX certificates from Azure Key Vault in .NET C#. The sample code shows how to load a certificate from Azure Key Vault and how to sign a PDF document with that certificate.

Sign PDF Documents with PFX Certificates from Azure Key Vault in .NET C#

This doesn't show how to sign specific signature fields of the document, but the entire document. A signature field is a predefined area in the PDF document that is specifically designed for placing a digital signature. Signing a signature field typically applies to that specific field or part of the document. When signing the entire document, the signature applies to the entire PDF file, including all of its contents. This is often used when a single person or entity needs to certify the entire document and ensure that no part of it has been tampered with after it has been signed. Of course, TX Text Control provides an API for both of these actions on a PDF document.

Conclusion

Signing PDF documents is a critical step in ensuring document security, trust, and compliance. By digitally signing your PDFs, you protect against tampering, build trust with recipients, and demonstrate your commitment to legal and regulatory standards. With the TX Text Control library, you can easily create applications that sign PDF documents, streamline your workflows, and ensure the integrity of your documents.