Sign a PDF with a DSC Token on Windows

A certificate, not a picture of your name

There is no draw-your-signature tool here. What gets written is a PAdES signature, SHA-256, over the document’s bytes: change one byte afterwards and the check fails. That property is the entire point, and a picture of your handwriting has none of it.

The certificate comes from your Windows personal store. A DSC token puts itself there — its middleware registers a cryptographic provider, the certificate shows up in the store while the token is plugged in, and the private key never leaves the token, which does the RSA itself and asks for its own PIN. That is the same route every established Windows signer takes, so there is no PKCS#11 setup on your side.

Sign the field that is yours

A government filing or a contract drawn up in advance arrives with one empty signature field per signatory, each one named. Sign anywhere else and you have a document that is technically signed, still has the other person’s field empty, and is no use for the thing it was drawn up for. So when named empty fields exist, the panel lists them and picks the first; putting a box of your own somewhere else is the last entry, and you have to choose it deliberately.

Then the certificate. Do not just take the first one — a TLS server certificate somebody installed years ago can sign a PDF perfectly well and is never what you meant. An expired one is refused outright, with the date, because a signature made with it would be rejected by anyone who checked.

The timestamp is the one thing that leaves the machine

Leave it off and no request is made. Turn it on and a separate helper program — the only binary in the product that contains any networking code at all — posts an RFC 3161 request to an authority you pick from the list. Nothing is pre-selected, because “the time authority you chose” stops being true the moment we choose one for you.

What crosses the wire is a hash of the signature value and a nonce. Not the document, not the document’s hash, not your name. The authority does see that a request arrived from your address at that moment, and it has its own data policy. Worth it when the signature must stay checkable after your certificate expires; skip it otherwise. The local-processing page sets out the whole boundary.

What an offline check can and cannot tell you

Sign, then read the verdict. The cryptography is checked here, on your machine, over the exact byte range the signature declares — so “intact” means the bytes have not moved since signing, and no amount of the page looking right survives a failure. Then Save, or Save a copy if the unsigned original still matters.

It does not ask anybody whether the certificate has been revoked. Revocation lists and OCSP are network requests, so revocation checking is switched off on purpose rather than left at a default that would quietly telephone a certificate authority on your behalf; the verdict says so in its own notes. Most readers that call a signature valid have asked someone. Ours is complete about the bytes and openly silent about revocation, so check with the recipient if their process needs more than that.

Common questions