Certifying a PDF and locking fields when you sign

An ordinary signature says "I signed this version." A certifying signature says something stronger: "this is my document, and here is what anyone may do to it from now on." PDF by Zaweba can make both, and it can also lock form fields as you sign, so the answers you're signing can't be changed afterwards.

Both features are about the same worry. Once a document is out of your hands, what happens to it? Certifying and locking let you answer that question in advance.

What certifying means

Certification is done as the first signature on a document. When you certify, you choose what may change afterwards. There are three levels: nothing; form filling and signing; or form filling and signing and also comments.

Nothing suits a finished document such as a published policy, a final report or a certificate of completion. Any change at all shows up as breaking the certification.

Form filling and signing suits a form you send out to be completed. People can fill it and sign it, but they can't alter the questions, the wording or the layout without it showing.

Adding comments suits a document going out for review where you want feedback but no edits to the content itself.

Because certification must come first, it belongs to whoever creates the document. If you send out forms, certify them before they go.

Locking fields

Locking is about signature fields on forms. When signing, you can lock all fields, chosen fields, or all but chosen fields, and optionally the whole document.

Lock all fields when your signature covers the whole form, such as an application you have completed. Lock chosen fields when your signature covers only part of it, for instance a manager approving the expenses section while leaving the finance section for someone else. All but chosen is the reverse, handy when only a few fields should stay open for later signers. Locking the whole document is the strongest choice, for the last signature on a document that should not change again.

Thinking about the order of signatures

On a document that collects several signatures, the order matters. The author certifies first, allowing form filling and signing. The first signer fills their section and signs, locking their fields. The next signer does the same with theirs. The last signer may lock the whole document.

Signatures are added as incremental updates, so each one covers its own version and the earlier ones stay valid. The signatures panel then shows each signature as valid, unknown or invalid, and lists the changes made after each one, so anyone can see the history.

What certifying and locking don't do

They don't stop someone with editing software from changing the file. What they do is make sure any change that breaks the rules shows up when signatures are checked. That is the point of digital signatures in general: they make changes visible rather than impossible.

They also don't hide anything. If a document should be kept private, password protection is the tool. If something must be removed, redaction is.

Choosing well

Pick the least permissive level that still lets people do their part. If recipients only need to fill and sign, don't also allow comments. Lock fields as you go on multi-person forms, so nobody can quietly change an earlier section. And test the routine once with a colleague before sending an important form to many people.

PDF by Zaweba does all of this offline, which matters when the documents being certified are contracts, approvals and records you'd rather keep on your own PC.