A family of Microsoft word processing software products for creating web, email, and print documents.
I assume you're referring to a Digital Signature as you would find in the Windows version of Word... Not handled the same on a Mac. See these existing Answers:
can I / how do i add a **digital** **signature** to a document in **word** ...
Need **digital** **signature** for **MS** **Office** **2011** on Mac - **Microsoft** Community