What is a certified PDF?

A certified PDF is one whose first digital signature is a certifying signature, which states what may change in the document afterwards. The choices are nothing at all, form filling and signing, or those plus comments. PDF by Zaweba can certify a document from its Sign menu and also lock all or chosen form fields. It's free and works offline on Windows.

In short, an ordinary signature says this person signed this version. A certifying signature adds: and here are the only changes allowed from now on.

How it differs from an ordinary signature

Any digital signature lets a reader check who signed and whether the document has been altered since. But PDFs can legitimately change after signing. A second person signs. Someone fills in a field. A reviewer adds a comment.

With ordinary signatures, those later changes are recorded, and a reader can look at them, but the first signer hasn't said in advance what they'd accept. A certifying signature settles that question. The author declares the rules when they sign, and any change outside those rules shows up as breaking the certification.

That's why only the first signature can certify. It sets the terms for everyone who comes after.

The three levels

Nothing may change suits a finished document: a final report, a certificate of completion, a published notice. Any change at all breaks the certification.

Form filling and signing suits a form you send out. Recipients can fill in fields and add their own signatures, but they can't alter the wording or layout without it showing.

Form filling, signing and comments adds annotation, for documents that will be reviewed or marked up but not rewritten.

Certifying a document

Finish the document first, because after certifying you're bound by your own rules. Then choose the Sign menu, pick certify as the first signature, and choose the level. Sign with your digital ID: a .pfx or .p12 file, a certificate in the Windows store, or a self-signed ID made in the app.

You can also lock fields. Choose to lock all fields, chosen fields, or all but the chosen ones, and optionally the whole document. Locking is useful when part of a form, such as the issuer's section, should be fixed while the rest stays open.

Checking a certified document

When you open a certified PDF, View, Signatures panel shows the certifying signature along with any later ones, lists changes made after each, and shows the signed version. That tells you whether later changes stayed within what the author allowed.

When to use it

Certify a document when you're the author, other people will interact with it after you, and you want those interactions limited and visible. For a document you're only agreeing to, an ordinary signature is enough.

A certified document can still be signed again by other people, as long as the level you chose allows signing. Each later signature is added as an incremental update, so the certifying signature stays valid and the Signatures panel shows the whole chain, one after another, with the changes made at each step.

For documents that must stay checkable for years, add a trusted timestamp and long-term validation information as well. PDF by Zaweba supports both, and keeps your digital ID on your own computer.