Revokable things can be cancelled. A revokable document can be changed or annulled by the person who creates it.
You'll often see the adjective revokable in legal documents, although it's often spelled revocable. A revokable trust, for example, is a legal entity that holds a person's assets in order to simplify the person's will — and because it's revokable, anything specified in the trust can be changed later. Political power is also revokable — it can be taken away from elected officials through the impeachment process.