Sign PDF Documents with a Certificate in C#

GdPicture.NET allows you to do the following:

Certify a PDF document.
Get certification properties.
Remove a certificate.
Add a certificate from other sources.

Certifying a PDF Document

To sign a PDF document with a certificate, follow these steps:

Create a digital ID or use an already created one.
Set the certificate contained in the digital ID stored in the PCKS#12 file or a Stream object with the SetSignatureCertificateFromP12 method.
Recommended: Specify the certificate information with the SetSignatureInfo method. It requires the following string parameters:
- Name — The person or authority certifying the document.
- Reason — The reason for certifying.
- Location — The physical location where the certificate was added.
- ContactInfo — The contact information.
Use the ApplySignature method to apply the certificate using the specified settings and save the PDF document to a file or a Stream object. This method requires the following parameters:
- OutputFileName or OutputStream — Either the path of the output file or a Stream object.
- SignatureMode — A member of the PdfSignatureMode enumeration that specifies the electronic signature technology used in the process.
- Linearization — A Boolean value that specifies if the output PDF document is linearized.

You can only add digital signatures to non-encrypted documents.

To certify a PDF document, use the following code:

using GdPicturePDF gdPicturePDF = new GdPicturePDF();
gdPicturePDF.LoadFromFile(@"C:\temp\source.pdf");
// Set the certificate from a file.
gdPicturePDF.SetSignatureCertificateFromP12(@"C:\temp\certificate.pfx", "pspdfkit");
// Add additional signature information.
gdPicturePDF.SetSignatureInfo("John Smith", "Confidential", "Vienna (Austria)",
    "[email protected]");
// Save the output to a file.
gdPicturePDF.ApplySignature(@"C:\temp\output.pdf",
    PdfSignatureMode.PdfSignatureModeAdobePPKMS, false);

Using gdPicturePDF As GdPicturePDF = New GdPicturePDF()
    gdPicturePDF.LoadFromFile("C:\temp\source.pdf")
    ' Set the certificate from a file.
    gdPicturePDF.SetSignatureCertificateFromP12("C:\temp\certificate.pfx", "pspdfkit")
    ' Add additional signature information.
    gdPicturePDF.SetSignatureInfo("John Smith", "Confidential", "Vienna (Austria)", "[email protected]")
    ' Save the output to a file.
    gdPicturePDF.ApplySignature("C:\temp\output.pdf", PdfSignatureMode.PdfSignatureModeAdobePPKMS, False)
End Using

Used Methods

Related Topics

Load a File

Additional Certificate Settings

The list below contains methods that provide additional settings when using a certificate. Use them after the SetSignatureCertificateFromP12 method and before the ApplySignature method:

The SetSignatureValidationMark method adds the validation icon inside the certificate with the SetSignatureValidationMark method.
The SetSignatureCertificationLevel method specifies the certificate’s certification level. It uses the PdfSignatureCertificationLevel enumeration as its parameter. This parameter allows you to define the access permissions granted by the certificate.
The SetSignatureHash method sets the hash algorithm used in the signing. It uses the PdfSignatureHash enumeration as its parameter.
The SetSignatureTimestampInfo method sets the timestamp information.

Getting the Certificate Properties

To get the properties of a certificate inside a PDF document, follow these steps:

Use the GetSignatureCount method to get the total number of signatures.
Loop through all signatures and use the GetSignatureProperties method. It requires the signature index and the following list of output reference parameters:
- SignatureName — The name of the person or authority signing the document.
- SignatureReason — The reason for signing the document.
- SignatureLocation — The physical location where the signing took place.
- SignatureContactInfo — The contact information of the signer.
- SignatureDate — The time of signing as a string.
- StampLeft — The horizontal coordinate of the signature’s closest point to the currently defined origin. The returned value is expressed in the units specified by the SetMeasurementUnit method.
- StampTop — The vertical coordinate of the signature’s closest point to the currently defined origin. The returned value is expressed in the units specified by the SetMeasurementUnit method.
- StampWidth — The width of the signature’s bounding box, expressed in the current units defined by the SetMeasurementUnit method.
- StampHeight — The height of the signature’s bounding box, expressed in the current units defined by the SetMeasurementUnit method.
- StampPage — The page number where the signature is.
- DocumentValid — A Boolean value that specifies whether the document has been altered or corrupted since it was signed.
- CertificateValid — A Boolean value that specifies whether the certificate used is verified.
- CertificateFriendlyName — The name of the certificate’s owner.
- CertificateIssuer — The name of the authority that issued the certificate.
- CertificateNotBefore — The earliest time and date when the used certificate was valid.
- CertificateNotAfter — The time and date after which the used certificate is no longer valid.
- CertificateSubject — The entity the used certificate belongs to (a person or an organization).
- CertificateVersion — The version of the used certificate.
- SigningTime — The date and time when the document was signed. Only use this value when the time of signing isn’t available in the signature.
- SignatureLevel — A member of the PdfSignatureCertificationLevel enumeration that represents the level of the signature certification.

If you have only one certificate in a PDF document, you can skip the GetSignatureCount method and use the GetSignatureProperties method with the signature index set to 0 as its parameter.

To list the properties of all certificates in a PDF document, use the following code:

using GdPicturePDF gdPicturePDF = new GdPicturePDF();
gdPicturePDF.LoadFromFile(@"C:\temp\source.pdf");
// Initiate all reference parameters.
string SignatureName = "", SignatureReason = "", SignatureLocation = "", SignatureContactInfo = "";
string SignatureDate = "", CertificateFriendlyName = "", CertificateIssuer = "", CertificateSubject = "";
float StampLeft = 0, StampTop = 0, StampWidth = 0, StampHeight = 0;
int StampPage = 0, CertificateVersion = 0;
bool DocumentValid = false, CertificateValid = false;
DateTime CertificateNotBefore = new DateTime();
DateTime CertificateNotAfter = new DateTime();
DateTime SigningTime = new DateTime();
PdfSignatureCertificationLevel SignatureLevel = PdfSignatureCertificationLevel.NotCertified;

// Get the total amount of certificates.
int signatureCount = gdPicturePDF.GetSignatureCount();
for (int i = 0; i <= signatureCount - 1; i++)
{
    // Get the properties of a certificate.
    gdPicturePDF.GetSignatureProperties(i,
        ref SignatureName,
        ref SignatureReason,
        ref SignatureLocation,
        ref SignatureContactInfo,
        ref SignatureDate,
        ref StampLeft,
        ref StampTop,
        ref StampWidth,
        ref StampHeight,
        ref StampPage,
        ref DocumentValid,
        ref CertificateValid,
        ref CertificateFriendlyName,
        ref CertificateIssuer,
        ref CertificateNotBefore,
        ref CertificateNotAfter,
        ref CertificateSubject,
        ref CertificateVersion,
        ref SigningTime,
        ref SignatureLevel);
    // Write the certificate name, reason, and signing date to the console.
    Console.WriteLine("Signature nr {0}:\n- Name: {1}\n- Reason: {2}\n- Date Signed: {3}",
       i, SignatureName, SignatureReason, SignatureDate);
}

Using gdPicturePDF As GdPicturePDF = New GdPicturePDF()
    gdPicturePDF.LoadFromFile("C:\temp\source.pdf")
    ' Initiate all reference parameters.
    Dim SignatureName = "", SignatureReason = "", SignatureLocation = "", SignatureContactInfo = ""
    Dim SignatureDate = "", CertificateFriendlyName = "", CertificateIssuer = "", CertificateSubject = ""
    Dim StampLeft As Single = 0, StampTop As Single = 0, StampWidth As Single = 0, StampHeight As Single = 0
    Dim StampPage = 0, CertificateVersion = 0
    Dim DocumentValid = False, CertificateValid = False
    Dim CertificateNotBefore As Date = New DateTime()
    Dim CertificateNotAfter As Date = New DateTime()
    Dim SigningTime As Date = New DateTime()
    Dim SignatureLevel As PdfSignatureCertificationLevel = PdfSignatureCertificationLevel.NotCertified

    ' Get the total amount of certificates.
    Dim signatureCount As Integer = gdPicturePDF.GetSignatureCount()
    For i = 0 To signatureCount - 1
        ' Get the properties of a certificate.
        gdPicturePDF.GetSignatureProperties(i,
            SignatureName,
            SignatureReason,
            SignatureLocation,
            SignatureContactInfo,
            SignatureDate,
            StampLeft,
            StampTop,
            StampWidth,
            StampHeight,
            StampPage,
            DocumentValid,
            CertificateValid,
            CertificateFriendlyName,
            CertificateIssuer,
            CertificateNotBefore,
            CertificateNotAfter,
            CertificateSubject,
            CertificateVersion,
            SigningTime,
            SignatureLevel)
        ' Write the certificate name, reason, and signing date to the console.
        Console.WriteLine("Signature nr {0}:" & vbLf & "- Name: {1}" & vbLf & "- Reason: {2}" & vbLf & "- Date Signed: {3}",
            i, SignatureName, SignatureReason, SignatureDate)
    Next
End Using

Used Methods

Related Topics

Load a File

Removing a Certificate from a PDF Document

To remove a certificate, use the RemoveSignature method. It requires only the signature index as its parameter. Use the GetSignatureCount method to get the total number of signatures.

If you have only one certificate in a PDF document, you can skip the GetSignatureCount method and use the RemoveSignature method with the signature index set to 0 as its parameter.

To delete all certificates, use the following code:

using GdPicturePDF gdPicturePDF = new GdPicturePDF();
gdPicturePDF.LoadFromFile(@"C:\temp\source.pdf");
// Get the total amount of certificates.
int signatureCount = gdPicturePDF.GetSignatureCount();
for (int i = 0; i <= signatureCount - 1; i++)
{
    // Remove the certificate.
    gdPicturePDF.RemoveSignature(0);
}
gdPicturePDF.SaveToFile(@"C:\temp\output.pdf");

Using gdPicturePDF As GdPicturePDF = New GdPicturePDF()
    gdPicturePDF.LoadFromFile("C:\temp\source.pdf")
    ' Get the total amount of certificates.
    Dim signatureCount As Integer = gdPicturePDF.GetSignatureCount()
    For i = 0 To signatureCount - 1
        ' Remove the certificate.
        gdPicturePDF.RemoveSignature(0)
    Next

    gdPicturePDF.SaveToFile("C:\temp\output.pdf")
End Using

Used Methods

Related Topics

Certifying a PDF Document from Other Sources

To add a certificate from sources other than a PFX file, such as a smart card or a Windows certificate store, use the following methods: