Explanation:

- Robbery: This involves taking property from someone with intention to permanently deprive them of it using violence or threat of violence. Not applicable here.

- Dacoity: This is similar to robbery but involves five or more people collectively committing the crime. Not relevant here as the scenario involves only A and Z.

- Theft: This is the unauthorized taking of someone's property with the intent of permanently depriving the owner of it. This doesn't involve inducing someone under fear to sign something.

- Extortion: This involves coercing someone into doing something, like signing a document, by putting them in fear of harm. This fits the described scenario.