Protect PDF Via Digital Signature Using Spire.PDF

Mozart He

25 Comments

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Arun K Pushpakaran5y ago
How can i get the pfx file?
shu ber8y ago
How can I get the IDnumber of the card owner?
Cris Fabela9y ago
Can we put multiple digital signature inside?
- Sarvjit Singh9y ago
  Yes, Spire.PDF supports muliple digital signature. I failed to send the code with format. Send mail to [email protected] for the code snippets and temporary license file of Spire.PDF.
Manthan Patel9y ago
How can i use .cer file as my certificate? I am having certificate int ePass2003Auto
- Sarvjit Singh9y ago
  You need to generate your .cer file as a pfx file to use it as a certification document.
kushal kale10y ago
I get error while creating signature at "doc.SaveToFile("sample.pdf");"... Error : File not found.
Harshad Pansuriya11y ago
Nice Sir
- Mozart He11y ago
  Thank you for reading and commenting.
Humayun Kabir Mamun11y ago
Nice...
- Mozart He11y ago
  Thank you.
Pankaj Kumar Choudhary11y ago
Thanks You sir to introduce us with such a nice tool..........
- Mozart He11y ago
  The pleasure is mine, Sir, thank you for reading and comment.
Santhakumar Munuswamy11y ago
Thanks for nice article
- Mozart He11y ago
  Thanks.
Mohammed Ibrahim11y ago
nice share
- Mozart He11y ago
  Thank you!
Rajeesh Menoth11y ago
Nice Share
- Mozart He11y ago
  Thank you very much for your comment!
Rakesh11y ago
Good one
- Mozart He11y ago
  Thank you, Sir.
Ankit Bansal11y ago
thanks for sharing..
- Mozart He11y ago
  Thank you so much for your comment.
Karthikeyan K11y ago
Thanks for sharing...
- Mozart He11y ago
  Thank you for reading, Sir.

Background

Data security becomes more and more important and essential when the cloud service and Internet are widely used in every aspect of our daily work, especially for the most common used file formats, such as PDF, Word, Excel and PowerPoint documents that may contain confidential context or intellectual property. In this way, we need to take some effective measures to protect those documents. There are some system-level security solutions for the document database, while rarely solutions for documents themselves. And we know that we can encrypt the PDF files with the password to protect the PDF file, but the password can be decrypted easily. This article will focus on introducing a better solution with higher security level namely securing PDF via PDF digital signature using a Free Spire.PDF for .NET. With the digital signature, we can confirm the identity of the author, and ensure the integrity of the transmission process. And that’s why digital signature has become a popular way to protect PDF file from editing and tampering.

In this tutorial, I focus on introducing PDF visible digital signature with the following parts:

Create a visible digital signature to PDF.
Get and verify the digital signature.

Preparation

If you are interested and want to try the PDF digital signature in C#, download free Spire.PDF on E-iceblue website or Nuget and install it. It is simple and clean. When you finish with the installation, you can go to "SampleCenter" and API Help, which gives you a brief and clear information for the usage of free Spire.PDF

Tools we need

Visual Studio

Spire.PDF has a bin folder, which contains .NET2.0, .NET3.5, .NET4.0 and NET4.0 ClientProfile. Please add the correct .dll based on your projects. Here I used .NET 4.0

Figure 1: Spire PDF

Part 1: C# code snippet to create visible digital signature

Step 1: Load a PDF file and certificate.

PdfDocument doc = new PdfDocument();
doc.LoadFromFile("test.pdf");
PdfCertificate cert = new PdfCertificate("Demo.pfx", "e-iceblue");

Step 2: Create a signature and set its position.

var signature = new PdfSignature(doc, doc.Pages[0], cert, "Requestd1");
signature.Bounds = new RectangleF(new PointF(280, 600), new SizeF(260, 90));

Step 3: Set the property for displaying the signature.

signature.IsTag = true;

Step 4: Fill the contents of the signature.

signature.DigitalSignerLable = "Digitally signed by";
signature.DigitalSigner = "Harry Hu for Test";
signature.DistinguishedName = "DN:";
signature.LocationInfoLabel = "Location:";
signature.LocationInfo = "London";
signature.ReasonLabel = "Reason: ";
signature.Reason = "Le document est certifie";
signature.DateLabel = "Date: ";
signature.Date = DateTime.Now;
signature.ContactInfoLabel = "Contact: ";
signature.ContactInfo = "123456789";
signature.Certificated = false;

Step 5: Set the document permission of the signature.

signature.DocumentPermissions = PdfCertificationFlags.ForbidChanges;

Step 6: Save the document to file in PDF format.

doc.SaveToFile("sample.pdf");

Please check the effective screenshot of the digital signature visible.

Figure 2: Digital Signature

Part 2: Getting and verifying the digital signature in PDF

Step 1: Load a PDF file with digital signature that created in part 1.

string filename = "sample.pdf";

Step 2: Get all the signatures from the PDF.

List < PdfSignature > signatures = new List < PdfSignature > ();
doc.LoadFromFile(filename);
var form = (PdfFormWidget) doc.Form;
for (int i = 0; i < form.FieldsWidget.Count; ++i)
{
var field = form.FieldsWidget[i] as PdfSignatureFieldWidget;
if (field != null && field.Signature != null)
{
PdfSignature signature1 = field.Signature;
signatures.Add(signature);
}
}

Step 3: Get the first signature.

PdfSignature signatureOne = signatures[0];
Verify the signature: try
{
bool bSignature = signatureOne.VerifySignature();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
Console.ReadLine();
}

Step 4: Get the certification of signature.

X509Certificate2 certificate = signatureOne.Certificate as X509Certificate2;

Step 5: Get the date of signature.

DateTime date = signatureOne.Date;

Step 6: Get the date on which the signature starts and ends valid.

DateTime validStart = certificate.NotBefore;
DateTime validEnd = certificate.NotAfter;

Step 7: Get the version of the certificate.

int version = certificate.Version;

Step 8: Get the subject distinguished name from the certificate.

string subject = certificate.Subject;

Please check the effective screenshot;.

Figure 3: Screenshot

Conclusion

By now, we have set the digital signature for PDF to increase its security level using free Spire.PDF. This free version meets the limited demand of my project. It also supports other features such as converting HTML, RTF, XPS, Text and Image to PDF. If your project is not that big and you need a quick solution, you could try it.

Thank you for reading and I hope this article helps.