In the legitimate software world, when you buy Microsoft Office, you receive a unique 25-character product key. You enter this key, Microsoft’s servers verify it, and your software is activated.
Most "pre-activated" installers found on third-party websites or from unauthorized technicians are pirated versions. These have been modified by hackers to bypass Microsoft's licensing checks, usually using tools like KMS activators or "cracks". The True Risks of Using Pirated Pre-Activated Office ms office pre activated