.NET Core C# Requires Chilkat v11.7.0+

Encrypt and Sign a PDF, and Sign an Encrypted PDF

See more PDF Protection Examples

Demonstrates signing together with encryption. A pending encrypt is applied by SignPdf before it signs, so one call produces a PDF that is both encrypted and signed. A PDF that is already encrypted can be signed too, and stays encrypted. When it was opened with only the user password its permissions decide: adding a signature field needs both the modify and the annotate permission. Loading the PDF with its owner password lifts that. .NET Core C#

bool success = false;

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  The PDF used in this example is available at two_page_memo.pdf

//  The signing certificate, with its private key.
Chilkat.Cert cert = new Chilkat.Cert();
success = cert.LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx","secret");
if (success == false) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

Chilkat.Pdf pdf = new Chilkat.Pdf();
success = pdf.LoadFile("qa_data/pdf/two_page_memo.pdf");
if (success == false) {
    Debug.WriteLine(pdf.LastErrorText);
    return;
}

//  Encrypt with AES-256 and do not permit modifying.
pdf.UserPassword = "user-secret";
pdf.OwnerPassword = "owner-secret";
Chilkat.JsonObject json = new Chilkat.JsonObject();
json.UpdateBool("permissions.modify",false);
Chilkat.JsonObject jsonOut = new Chilkat.JsonObject();
success = pdf.Protection("encrypt",json,jsonOut);
if (success == false) {
    Debug.WriteLine(pdf.LastErrorText);
    return;
}

//  The encryption is still pending.  SignPdf applies it first and signs the encrypted result.
success = pdf.SetSigningCert(cert);
if (success == false) {
    Debug.WriteLine(pdf.LastErrorText);
    return;
}

Chilkat.JsonObject sigOpts = new Chilkat.JsonObject();
sigOpts.UpdateBool("invisibleSignature",true);
sigOpts.UpdateInt("signingCertificateV2",1);
sigOpts.UpdateInt("signingTime",1);
success = pdf.SignPdf(sigOpts,"qa_output/memo_encrypted_signed.pdf");
if (success == false) {
    Debug.WriteLine(pdf.LastErrorText);
    return;
}

//  The result is encrypted and signed.
Chilkat.Pdf check = new Chilkat.Pdf();
check.UserPassword = "user-secret";
success = check.LoadFile("qa_output/memo_encrypted_signed.pdf");
if (success == false) {
    Debug.WriteLine(check.LastErrorText);
    return;
}

Chilkat.JsonObject empty = new Chilkat.JsonObject();
Chilkat.JsonObject info = new Chilkat.JsonObject();
success = check.Protection("getInfo",empty,info);
if (success == false) {
    Debug.WriteLine(check.LastErrorText);
    return;
}

Debug.WriteLine("algorithm: " + info.StringOf("loaded.algorithm"));
Debug.WriteLine("signatures: " + Convert.ToString(check.NumSignatures));
Chilkat.JsonObject sigInfo = new Chilkat.JsonObject();
bool verified = check.VerifySignature(0,sigInfo);
Debug.WriteLine("signature verifies: " + Convert.ToString(verified));

//  Signing an encrypted PDF.  This one was opened with only the user password, and its
//  permissions do not allow modifying, so another signature is refused.
success = check.SetSigningCert(cert);
if (success == false) {
    Debug.WriteLine(check.LastErrorText);
    return;
}

success = check.SignPdf(sigOpts,"qa_output/memo_signed_twice.pdf");
if (success == false) {
    Debug.WriteLine("A second signature was refused: the permissions do not allow it.");
}

//  Loaded with the owner password, the same PDF can be signed.  It stays encrypted, and the
//  first signature stays valid because the new one is added as an incremental update.
Chilkat.Pdf owner = new Chilkat.Pdf();
owner.UserPassword = "user-secret";
owner.OwnerPassword = "owner-secret";
success = owner.LoadFile("qa_output/memo_encrypted_signed.pdf");
if (success == false) {
    Debug.WriteLine(owner.LastErrorText);
    return;
}

success = owner.SetSigningCert(cert);
if (success == false) {
    Debug.WriteLine(owner.LastErrorText);
    return;
}

success = owner.SignPdf(sigOpts,"qa_output/memo_signed_twice.pdf");
if (success == false) {
    Debug.WriteLine(owner.LastErrorText);
    return;
}

Chilkat.Pdf twice = new Chilkat.Pdf();
twice.UserPassword = "user-secret";
success = twice.LoadFile("qa_output/memo_signed_twice.pdf");
if (success == false) {
    Debug.WriteLine(twice.LastErrorText);
    return;
}

Debug.WriteLine("signatures after signing with owner rights: " + Convert.ToString(twice.NumSignatures));
verified = twice.VerifySignature(0,sigInfo);
Debug.WriteLine("first signature still verifies: " + Convert.ToString(verified));
verified = twice.VerifySignature(1,sigInfo);
Debug.WriteLine("second signature verifies: " + Convert.ToString(verified));

//  Sample output:

//  algorithm: aes-256
//  signatures: 1
//  signature verifies: True
//  A second signature was refused: the permissions do not allow it.
//  signatures after signing with owner rights: 2
//  first signature still verifies: True
//  second signature verifies: True