Digitally Sign In PDF File
In this tutorial, we will walk you through the process of digitally signing in PDF file using Aspose.PDF for .NET. The digital signature guarantees the authenticity and integrity of the document, by adding a unique electronic fingerprint.
Step 1: Prerequisites
Before you begin, make sure you have the following prerequisites:
- Basic knowledge of the C# programming language
- Installing Visual Studio on your machine
- Aspose.PDF library for .NET installed
Step 2: Environment setup
To get started, follow these steps to set up your development environment:
- Open Visual Studio and create a new C# project.
- Import the required namespaces into your code file:
using Aspose.Pdf;
using Aspose.Pdf.Forms;
using System.Collections.Generic;
Step 3: Digital signature
The first step is to digitally sign the PDF file. The provided code shows how to make a digital signature with Aspose.PDF for .NET.
string dataDir = "YOUR DOCUMENTS DIRECTORY";
string pbxFile = "";
string inFile = dataDir + @"DigitallySign.pdf";
string outFile = dataDir + @"DigitallySign_out.pdf";
using (Document document = new Document(inFile))
{
using (PdfFileSignature signature = new PdfFileSignature(document))
{
PKCS7 pkcs = new PKCS7(pbxFile, "WebSales");
DocMDPSignature docMdpSignature = new DocMDPSignature(pkcs, DocMDPAccessPermissions.FillingInForms);
System.Drawing.Rectangle rect = new System.Drawing.Rectangle(100, 100, 200, 100);
signature.SignatureAppearance = dataDir + @"aspose-logo.jpg";
signature.Certify(1, "Reason for signing", "Contact", "Location", true, rect, docMdpSignature);
signature.Save(outFile);
}
}
This code loads a PDF file, creates a digital signature with a specified appearance, then saves the PDF file with the added signature.
Step 4: Signature Verification
After adding the digital signature, you can check if the PDF file contains a valid signature.
using(Document document = new Document(outFile))
{
using (PdfFileSignature signature = new PdfFileSignature(document))
{
IList<string> sigNames = signature. GetSignNames();
if (sigNames.Count > 0)
{
if (signature.VerifySigned(sigNames[0] as string))
{
if (signature.IsCertified)
{
if (signature.GetAccessPermissions() == DocMDPAccessPermissions.FillingInForms)
{
// Do something
}
}
}
}
}
}
This code verifies the first signature of the PDF file and performs additional actions if the signature is certified and has specific permissions.
Sample source code for Digitally Sign using Aspose.PDF for .NET
try
{
// The path to the documents directory.
string dataDir = "YOUR DOCUMENTS DIRECTORY";
string pbxFile = "";
string inFile = dataDir + @"DigitallySign.pdf";
string outFile = dataDir + @"DigitallySign_out.pdf";
using (Document document = new Document(inFile))
{
using (PdfFileSignature signature = new PdfFileSignature(document))
{
PKCS7 pkcs = new PKCS7(pbxFile, "WebSales"); // Use PKCS7/PKCS7Detached objects
DocMDPSignature docMdpSignature = new DocMDPSignature(pkcs, DocMDPAccessPermissions.FillingInForms);
System.Drawing.Rectangle rect = new System.Drawing.Rectangle(100, 100, 200, 100);
// Set signature appearance
signature.SignatureAppearance = dataDir + @"aspose-logo.jpg";
// Create any of the three signature types
signature.Certify(1, "Signature Reason", "Contact", "Location", true, rect, docMdpSignature);
// Save output PDF file
signature.Save(outFile);
}
}
using (Document document = new Document(outFile))
{
using (PdfFileSignature signature = new PdfFileSignature(document))
{
IList<string> sigNames = signature.GetSignNames();
if (sigNames.Count > 0) // Any signatures?
{
if (signature.VerifySigned(sigNames[0] as string)) // Verify first one
{
if (signature.IsCertified) // Certified?
{
if (signature.GetAccessPermissions() == DocMDPAccessPermissions.FillingInForms) // Get access permission
{
// Do something
}
}
}
}
}
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Conclusion
Congratulation ! You have successfully performed a digital signature on a PDF file using Aspose.PDF for .NET. This tutorial covered the step-by-step process, from adding the digital signature to verifying its validity. You can now use this feature to secure your PDF files with digital signatures.
FAQ’s
Q: What is the purpose of this tutorial?
A: This tutorial guides you through the process of digitally signing a PDF file using Aspose.PDF for .NET. Digital signatures add an electronic fingerprint to ensure the authenticity and integrity of the document.
Q: What prerequisites are required before starting?
A: Before you begin, ensure you have a basic understanding of the C# programming language, have Visual Studio installed, and have the Aspose.PDF library for .NET installed.
Q: How do I set up the development environment?
A: Follow the provided steps to set up your development environment, including creating a new C# project in Visual Studio, and importing the required namespaces.
Q: How do I add a digital signature to a PDF file?
A: The provided sample code demonstrates how to load a PDF file, create a digital signature, specify appearance, and save the signed PDF file. The digital signature is added using the Certify method of the PdfFileSignature object.
Q: How do I verify the validity of a digital signature?
A: After adding the digital signature, you can use the sample code to verify the validity of the signature. It checks if the signature is certified and has specific access permissions.
Q: What does the PKCS7 object represent?
A: The PKCS7 object is used to provide the cryptographic functionality for digital signatures. It is used to create the digital signature in the provided sample code.
Q: Can I customize the appearance of the digital signature?
A: Yes, you can customize the appearance of the digital signature by specifying the path to an image in the SignatureAppearance property of the PdfFileSignature object.
Q: What happens if the signature is not valid?
A: If the signature is not valid, the verification process will fail, and the corresponding actions within the verification code block will not be executed.
Q: How can I ensure the security of my digital signatures?
A: Digital signatures are secure by design and use cryptographic techniques to ensure authenticity and integrity. Ensure that you keep your private key secure and follow best practices for handling digital signatures.
Q: Can I add multiple digital signatures to a PDF?
A: Yes, you can add multiple digital signatures to a PDF file using the PdfFileSignature object’s Sign or Certify methods. Each signature will have its own appearance and configuration.
