Add PDF Digital Signatures
The following example shows how to convert a PowerPoint presentation to a digitally signed PDF file with visual representation in C# and VB.NET, using GemBox.Presentation.
using GemBox.Presentation;
using System.IO;
class Program
{
static void Main()
{
// If using the Professional version, put your serial key below.
ComponentInfo.SetLicense("FREE-LIMITED-KEY");
var presentation = PresentationDocument.Load("%InputFileName%");
// Create visual representation of digital signature on the first slide.
Picture signature = null;
using (var stream = File.OpenRead("%#GemBoxSignature.png%"))
signature = presentation.Slides[0].Content.AddPicture(
PictureContentType.Png, stream, 25, 15, 4, 1, LengthUnit.Centimeter);
var options = new PdfSaveOptions()
{
DigitalSignature =
{
CertificatePath = "%InputDigitalId%",
CertificatePassword = "GemBoxPassword",
Signature = signature,
IsAdvancedElectronicSignature = true
}
};
presentation.Save("PDF Digital Signature.pdf", options);
}
}
Imports GemBox.Presentation
Imports System.IO
Module Program
Sub Main()
' If using the Professional version, put your serial key below.
ComponentInfo.SetLicense("FREE-LIMITED-KEY")
Dim presentation = PresentationDocument.Load("%InputFileName%")
' Create visual representation of digital signature on the first slide.
Dim signature As Picture = Nothing
Using stream = File.OpenRead("%#GemBoxSignature.png%")
signature = presentation.Slides(0).Content.AddPicture(
PictureContentType.Png, stream, 25, 15, 4, 1, LengthUnit.Centimeter)
End Using
Dim options As New PdfSaveOptions() With
{
.DigitalSignature = New PdfDigitalSignatureSaveOptions() With
{
.CertificatePath = "%InputDigitalId%",
.CertificatePassword = "GemBoxPassword",
.Signature = signature,
.IsAdvancedElectronicSignature = True
}
}
presentation.Save("PDF Digital Signature.pdf", options)
End Sub
End Module
A PDF digital signature enables you to authenticate a PDF file to establish that the sender of the file is who they say they are and the content of the PDF file has not been tampered with.
Before reviewing the output of the following examples in your Adobe Acrobat Reader, please read the Digital ID notes and Time-stamp notes.
The next example shows another solution for this by using GemBox.Presentation and GemBox.Pdf components together to create PDF Advanced Electronic Signature (PAdES) of B-LTA level that embeds all validation-related information in the PDF file thus making the signature LTV enabled. The following example shows how to create a digitally signed PDF file with PAdES B-LTA level signature. PDF Advanced Electronic Signature (PAdES) is an electronic signature in a PDF file that has met the requirements set forth by the eIDAS regulation on electronic identification and trust services for electronic transactions in the European Single Market. With GemBox.Presentation and GemBox.Pdf, you can create PAdES baseline signatures as specified in ETSI EN 319 142-1. PAdES B-LTA level signature has the following characteristics: PAdES B-LTA level may help to validate the signature beyond any event that may limit its validity. This level is recommended for Qualified Electronic Signatures. Digital ID files used in the preceding examples are part of a simple Public Key Infrastructure (PKI) created just for this demonstration which contains the following hierarchy of certificates and CRLs: To get a valid signature in your Adobe Acrobat Reader as seen in the screenshots above, you will have to add GemBoxCA.crt certificate to the list of Trusted Certificates using the following steps: Otherwise, to get a valid signature in any Adobe Acrobat Reader, your digital ID would have to be an AATL-enabled signing credential. The Time Stamp Authority used in the preceding example is freeTSA.org. The root certificate of the freeTSA.org Public Key Infrastructure (PKI) is tsa.crt. To get a valid signature timestamp in your Adobe Acrobat Reader as seen in the screenshot from above, you will have to add the tsa.crt certificate to the list of Trusted Certificates using the same steps as in the previous subsection.PAdES signature (LTV enabled)
using GemBox.Pdf.Forms;
using GemBox.Pdf.Security;
using GemBox.Presentation;
using System.IO;
class Program
{
static void Main()
{
// If using the Professional version, put your serial key below.
ComponentInfo.SetLicense("FREE-LIMITED-KEY");
var presentation = PresentationDocument.Load("%InputFileName%");
// Create visual representation of digital signature on the first slide.
Picture signature = null;
using (var stream = File.OpenRead("%#GemBoxSignature.png%"))
signature = presentation.Slides[0].Content.AddPicture(
PictureContentType.Png, stream, 25, 15, 4, 1, LengthUnit.Centimeter);
// If using the Professional version, put your serial key below.
GemBox.Pdf.ComponentInfo.SetLicense("FREE-LIMITED-KEY");
// Get a digital ID from PKCS#12/PFX file.
var digitalId = new PdfDigitalId("%InputDigitalId%", "GemBoxPassword");
// Create a PDF signer that will create PAdES B-LTA level signature.
var signer = new PdfSigner(digitalId);
// PdfSigner should create CAdES-equivalent signature.
signer.SignatureFormat = PdfSignatureFormat.CAdES;
// PdfSigner will embed a timestamp created by freeTSA.org Time Stamp Authority in the signature.
signer.Timestamper = new PdfTimestamper("https://freetsa.org/tsr");
// Make sure that all properties specified on PdfSigner are according to PAdES B-LTA level.
signer.SignatureLevel = PdfSignatureLevel.PAdES_B_LTA;
// Inject PdfSigner from GemBox.Pdf into
// PdfDigitalSignatureSaveOptions from GemBox.Presentation.
var signatureOptions = PdfDigitalSignatureSaveOptions.FromSigner(
() => signer.SignatureFormat.ToString(),
() => signer.EstimatedSignatureContentsLength,
signer.ComputeSignature);
signatureOptions.Signature = signature;
var options = new PdfSaveOptions()
{
DigitalSignature = signatureOptions
};
presentation.Save("PAdES B-LTA.pdf", options);
using (var pdfDocument = GemBox.Pdf.PdfDocument.Load("PAdES B-LTA.pdf"))
{
var signatureField = (PdfSignatureField)pdfDocument.Form.Fields[0];
// Download validation-related information for the signature and the signature's timestamp and embed it in the PDF file.
// This will make the signature "LTV enabled".
pdfDocument.SecurityStore.AddValidationInfo(signatureField.Value);
// Add an invisible signature field to the PDF document that will hold the document timestamp.
var timestampField = pdfDocument.Form.Fields.AddSignature();
// Initiate timestamping of a PDF file with the specified timestamper.
timestampField.Timestamp(signer.Timestamper);
// Save any changes done to the PDF file that were done since the last time Save was called and
// finish timestamping of a PDF file.
pdfDocument.Save();
}
}
}
Imports GemBox.Pdf.Forms
Imports GemBox.Pdf.Security
Imports GemBox.Presentation
Imports System.IO
Module Program
Sub Main()
' If using the Professional version, put your serial key below.
ComponentInfo.SetLicense("FREE-LIMITED-KEY")
Dim presentation = PresentationDocument.Load("%InputFileName%")
' Create visual representation of digital signature on the first slide.
Dim signature As Picture = Nothing
Using stream = File.OpenRead("%#GemBoxSignature.png%")
signature = presentation.Slides(0).Content.AddPicture(
PictureContentType.Png, stream, 25, 15, 4, 1, LengthUnit.Centimeter)
End Using
' If using the Professional version, put your serial key below.
GemBox.Pdf.ComponentInfo.SetLicense("FREE-LIMITED-KEY")
' Get a digital ID from PKCS#12/PFX file.
Dim digitalId = New PdfDigitalId("%InputDigitalId%", "GemBoxPassword")
' Create a PDF signer that will create PAdES B-LTA level signature.
Dim signer = New PdfSigner(digitalId)
' PdfSigner should create CAdES-equivalent signature.
signer.SignatureFormat = PdfSignatureFormat.CAdES
' PdfSigner will embed a timestamp created by freeTSA.org Time Stamp Authority in the signature.
signer.Timestamper = New PdfTimestamper("https://freetsa.org/tsr")
' Make sure that all properties specified on PdfSigner are according to PAdES B-LTA level.
signer.SignatureLevel = PdfSignatureLevel.PAdES_B_LTA
' Inject PdfSigner from GemBox.Pdf into
' PdfDigitalSignatureSaveOptions from GemBox.Presentation.
Dim signatureOptions = PdfDigitalSignatureSaveOptions.FromSigner(
Function() signer.SignatureFormat.ToString(),
Function() signer.EstimatedSignatureContentsLength,
Function(pdfFileStream) signer.ComputeSignature(pdfFileStream))
signatureOptions.Signature = signature
Dim options = New PdfSaveOptions() With
{
.DigitalSignature = signatureOptions
}
presentation.Save("PAdES B-LTA.pdf", options)
Using pdfDocument = GemBox.Pdf.PdfDocument.Load("PAdES B-LTA.pdf")
Dim signatureField = CType(pdfDocument.Form.Fields(0), PdfSignatureField)
' Download validation-related information for the signature and the signature's timestamp and embed it in the PDF file.
' This will make the signature "LTV enabled".
pdfDocument.SecurityStore.AddValidationInfo(signatureField.Value)
' Add an invisible signature field to the PDF document that will hold the document timestamp.
Dim timestampField = pdfDocument.Form.Fields.AddSignature()
' Initiate timestamping of a PDF file with the specified timestamper.
timestampField.Timestamp(signer.Timestamper)
' Save any changes done to the PDF file that were done since the last time Save was called and
' finish timestamping of a PDF file.
pdfDocument.Save()
End Using
End Sub
End Module
Digital ID notes
Time-stamp notes
