(.NET Core C#) PDF Sign Under Existing Signature
This example explains how sign a previously-signed PDF and place the signature appearance below the existing signature.
Note: This example requires Chilkat v9.5.0.85 or greater.
// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.
Chilkat.Pdf pdf = new Chilkat.Pdf();
// Load a PDF to be signed.
bool success = pdf.LoadFile("qa_data/pdf/sign_testing_4/hello_signed.pdf");
if (success == false) {
Debug.WriteLine(pdf.LastErrorText);
return;
}
// The PDF we'll be signing already has a signature added in Adobe Acrobat DC.
// It looks like this:
// (Notice the Adobe background logo, which is commonly what you'll see when a signature
// is created by Adobe Acrobat. Chilkat (obviously) does not create signatures using the Adobe
// logo because it would be a copyright violation.)
// Options for signing are specified in JSON.
Chilkat.JsonObject json = new Chilkat.JsonObject();
// In most cases, the signingCertificateV2 and signingTime attributes are required.
json.UpdateInt("signingCertificateV2",1);
json.UpdateInt("signingTime",1);
// To put our new signature underneath the existing signature, we have to specify the page
// where the existing signature is found, and then we can specify "under" for the "appearance.y"
json.UpdateInt("page",1);
json.UpdateString("appearance.y","under");
json.UpdateString("appearance.fontScale","10.0");
json.UpdateString("appearance.text[0]","Reason: Agreement Accepted by John");
json.UpdateString("appearance.text[1]","Date: current_dt");
// Load the signing certificate. (Use your own certificate.)
Chilkat.Cert cert = new Chilkat.Cert();
success = cert.LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx","secret");
if (success == false) {
Debug.WriteLine(cert.LastErrorText);
return;
}
// Tell the pdf object to use the certificate for signing.
success = pdf.SetSigningCert(cert);
if (success == false) {
Debug.WriteLine(pdf.LastErrorText);
return;
}
// Note: When adding an additional signature to a PDF, the existing signatures
// are validated, and this includes validating the certificates previously used to
// create the existing signatures. (A signature typically embeds the signing certs.)
// In some cases, the certificates and/or certs in the chain of authentication for
// existing signatures are not present, and are not available on the current system.
// In this case, you can skip the validation by setting this keyword in UncommonOptions:
pdf.UncommonOptions = "NO_VERIFY_CERT_SIGNATURES";
success = pdf.SignPdf(json,"qa_output/hello_signed.pdf");
if (success == false) {
Debug.WriteLine(pdf.LastErrorText);
return;
}
Debug.WriteLine("The PDF has been successfully cryptographically signed.");
// Here's a screenshot of the 2nd signature positioned under the 1st in Adobe Acrobat:
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