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(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.
#include <C_CkPdf.h>
#include <C_CkJsonObject.h>
#include <C_CkCert.h>
void ChilkatSample(void)
{
HCkPdf pdf;
BOOL success;
HCkJsonObject json;
HCkCert cert;
// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.
pdf = CkPdf_Create();
// Load a PDF to be signed.
success = CkPdf_LoadFile(pdf,"qa_data/pdf/sign_testing_4/hello_signed.pdf");
if (success == FALSE) {
printf("%s\n",CkPdf_lastErrorText(pdf));
CkPdf_Dispose(pdf);
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.
json = CkJsonObject_Create();
// In most cases, the signingCertificateV2 and signingTime attributes are required.
CkJsonObject_UpdateInt(json,"signingCertificateV2",1);
CkJsonObject_UpdateInt(json,"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"
CkJsonObject_UpdateInt(json,"page",1);
CkJsonObject_UpdateString(json,"appearance.y","under");
CkJsonObject_UpdateString(json,"appearance.fontScale","10.0");
CkJsonObject_UpdateString(json,"appearance.text[0]","Reason: Agreement Accepted by John");
CkJsonObject_UpdateString(json,"appearance.text[1]","Date: current_dt");
// Load the signing certificate. (Use your own certificate.)
cert = CkCert_Create();
success = CkCert_LoadPfxFile(cert,"qa_data/pfx/myPdfSigningCert.pfx","secret");
if (success == FALSE) {
printf("%s\n",CkCert_lastErrorText(cert));
CkPdf_Dispose(pdf);
CkJsonObject_Dispose(json);
CkCert_Dispose(cert);
return;
}
// Tell the pdf object to use the certificate for signing.
success = CkPdf_SetSigningCert(pdf,cert);
if (success == FALSE) {
printf("%s\n",CkPdf_lastErrorText(pdf));
CkPdf_Dispose(pdf);
CkJsonObject_Dispose(json);
CkCert_Dispose(cert);
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:
CkPdf_putUncommonOptions(pdf,"NO_VERIFY_CERT_SIGNATURES");
success = CkPdf_SignPdf(pdf,json,"qa_output/hello_signed.pdf");
if (success == FALSE) {
printf("%s\n",CkPdf_lastErrorText(pdf));
CkPdf_Dispose(pdf);
CkJsonObject_Dispose(json);
CkCert_Dispose(cert);
return;
}
printf("The PDF has been successfully cryptographically signed.\n");
// Here's a screenshot of the 2nd signature positioned under the 1st in Adobe Acrobat:
CkPdf_Dispose(pdf);
CkJsonObject_Dispose(json);
CkCert_Dispose(cert);
}
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