QuestPDF Sign PDF Documents vs IronPDF (Code Example)

A digital signature is a mathematical algorithm used to authenticate the identity of the signer and ensure the integrity of a document. It creates a unique identifier linked to the document, which is signed using a private key known only to the signer. To verify the authenticity of a digitally signed document, the recipient uses the public key to decrypt the signature and confirm its validity.

In this article, we will compare how to add digital signatures to PDF documents using QuestPDF and IronPDF libraries in C#. Both libraries offer robust features for PDF manipulation, including digital signature capabilities.

Why are Digital Signatures Important?

Digital signatures ensure that the content of a document hasn’t been tampered with and prove the signer’s identity. This provides a higher level of security compared to traditional signatures. Digital signatures are legally binding in many countries and are commonly used for contracts, agreements, and other legal documents.

Prerequisites

Before we start, make sure you have a basic understanding of C# and the .NET Framework. You’ll need to install both QuestPDF and IronPDF. QuestPDF can be installed from NuGet, and IronPDF can be downloaded from the IronPDF website or through the NuGet Package Manager.

You will also need to have a digital signature ready to go, and if you don't, there are many resources out there that help you create a new one.

Comparison on Adding Digital Signature to PDF Documents in C# Using QuestPDF vs IronPDF

Now let's take a closer look at these two libraries and how they handle the task of applying digital signatures to PDF documents.

QuestPDF is an open-source library focused on generating PDF documents using a fluent API for creating complex layouts thanks to its comprehensive layout engine. It’s less geared towards PDF manipulation but can be used in conjunction with other tools for signing PDFs. It also comes with a companion app that allows users to explore the document structure of their PDFs with ease, and utilizes a hot reload capability to provide you with live document previews without the need for code recompilation.

IronPDF is a robust .NET library that provides powerful features for PDF document generation, manipulating, and signing PDF documents. It’s designed for .NET developers looking for a comprehensive and easy-to-use solution. With IronPDF, you can easily encrypt PDF documents, add annotation, convert HTML to PDF, extract content, and more!

QuestPDF

QuestPDF doesn’t natively support digital signatures. However, you can combine it with other libraries (like BouncyCastle or PdfSharp) for this functionality. After generating your document with QuestPDF, you can sign it using a library that does offer PDF signing tools such as iTextSharp, but the QuestPDF library itself does not handle PDF signing.

It offers other basic forms of PDF security, in the form of PDF encryption, as well as advanced PDF creation and the ability to design PDF documents, so it can still be a viable option for those looking for a PDF library that is capable of handling basic PDF tasks without too many bells and whistles.

IronPDF

IronPDF offers a straightforward API for signing PDFs with a digital certificate. The following code demonstrates how to apply a digital signature to a PDF file using IronPDF.

using IronPdf;
using IronPdf.Signing;
using System.Security.Cryptography.X509Certificates;

public class Program
{
    static void Main(string[] args)
    {
        // Load an existing PDF document
        PdfDocument pdf = PdfDocument.FromFile("invoice.pdf");

        // Load a certificate from a .pfx file
        X509Certificate2 cert = new X509Certificate2("IronSoftware.pfx", "your-password", X509KeyStorageFlags.Exportable);

        // Create a PDF signature using the certificate
        var sig = new PdfSignature(cert);

        // Sign the PDF document
        pdf.Sign(sig);

        // Save the signed PDF document
        pdf.SaveAs("signed.pdf");
    }
}

using IronPdf;
using IronPdf.Signing;
using System.Security.Cryptography.X509Certificates;

public class Program
{
    static void Main(string[] args)
    {
        // Load an existing PDF document
        PdfDocument pdf = PdfDocument.FromFile("invoice.pdf");

        // Load a certificate from a .pfx file
        X509Certificate2 cert = new X509Certificate2("IronSoftware.pfx", "your-password", X509KeyStorageFlags.Exportable);

        // Create a PDF signature using the certificate
        var sig = new PdfSignature(cert);

        // Sign the PDF document
        pdf.Sign(sig);

        // Save the signed PDF document
        pdf.SaveAs("signed.pdf");
    }
}

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

Public Class Program
	Shared Sub Main(ByVal args() As String)
		' Load an existing PDF document
		Dim pdf As PdfDocument = PdfDocument.FromFile("invoice.pdf")

		' Load a certificate from a .pfx file
		Dim cert As New X509Certificate2("IronSoftware.pfx", "your-password", X509KeyStorageFlags.Exportable)

		' Create a PDF signature using the certificate
		Dim sig = New PdfSignature(cert)

		' Sign the PDF document
		pdf.Sign(sig)

		' Save the signed PDF document
		pdf.SaveAs("signed.pdf")
	End Sub
End Class

This code demonstrates how to digitally sign a PDF document using IronPDF and an X.509 certificate. First, it loads an existing PDF (invoice.pdf) into a PdfDocument object. Then, it loads a certificate from a .pfx file (IronSoftware.pfx) by providing the password (your-password) and setting the flag X509KeyStorageFlags.Exportable to allow exporting the certificate's private key if necessary.

Next, a PdfSignature object is created using the loaded certificate. This signature is then applied to the PDF document, effectively signing it. Finally, the signed PDF is saved as a new file called signed.pdf. This process ensures that the PDF is securely signed, verifying its authenticity and integrity.

How To Verify a Signature Using IronPDF

IronPDF also provides an easy way to verify digital signatures. You can call the VerifyPdfSignatures method to check the validity of the signatures in the document.

using IronPdf;

PdfDocument pdf = PdfDocument.FromFile("signed_test_document.pdf");

// Verify the digital signatures in the PDF document
bool isValid = pdf.VerifyPdfSignatures();
if (isValid)
{
    Console.WriteLine("The digital signature is valid.");
}
else
{
    Console.WriteLine("The digital signature is invalid or missing.");
}

using IronPdf;

PdfDocument pdf = PdfDocument.FromFile("signed_test_document.pdf");

// Verify the digital signatures in the PDF document
bool isValid = pdf.VerifyPdfSignatures();
if (isValid)
{
    Console.WriteLine("The digital signature is valid.");
}
else
{
    Console.WriteLine("The digital signature is invalid or missing.");
}

Imports IronPdf

Private pdf As PdfDocument = PdfDocument.FromFile("signed_test_document.pdf")

' Verify the digital signatures in the PDF document
Private isValid As Boolean = pdf.VerifyPdfSignatures()
If isValid Then
	Console.WriteLine("The digital signature is valid.")
Else
	Console.WriteLine("The digital signature is invalid or missing.")
End If

This method returns true if all signatures in the document are valid and false if any signature is invalid or missing.

Summary of Differences Between QuestPDF and IronPDF

Ease of Use: IronPDF provides a much simpler API for signing PDFs compared to QuestPDF. QuestPDF does not offer native support for digital signatures and requires external libraries (e.g., BouncyCastle) for this functionality. In contrast, IronPDF has built-in methods for signing and verifying PDFs, making it more straightforward to implement digital signatures.

Certificate Management: Both libraries can work with certificates, but IronPDF handles them directly through its built-in methods (e.g., SignWithFile), simplifying the process. It also allows you to specify signature permissions, which isn't offered by QuestPDF. Sign PDF documents with IronPDF in just a few lines of code.

Digital Signature Verification: IronPDF offers an easy-to-use method (VerifyPdfSignatures) to check the validity of digital signatures within PDFs, while QuestPDF lacks this feature and relies on external libraries for signature verification.

License & Cost: QuestPDF is an open-source library that is free to use. This comes with the cost of lacking advanced features such as digital signature support. IronPDF is free for development, and beyond this, it offers a range of pricing tiers for its commercial licensing to try it out before you buy.

Conclusion

In summary, while QuestPDF excels at creating PDFs with complex layouts, it lacks native support for digital signatures, requiring external libraries like BouncyCastle for this functionality. In contrast, IronPDF offers an integrated solution for signing and verifying digital signatures, providing a simpler and more efficient process.

For developers needing a complete PDF solution with built-in digital signature capabilities, IronPDF is the better choice, with a wide range of features, extensive documentation, and more. QuestPDF, however, remains a strong open-source option for PDF generation, but digital signing requires additional complexity. The decision ultimately depends on the project's needs and the desired level of simplicity.