Microsoft has never sold "lifetime" Office 365 subscriptions. If a deal sounds too good to be true, it almost certainly violates Microsoft's terms of service or involves stolen credentials.
First, navigate to the official setup website, usually setup.office.com or microsoft365.com/setup . You will be prompted to sign in with a Microsoft account. This is a critical step: the product key will be permanently tied to the email address you use to sign in. If you lose access to this email, you may lose access to your software license. Once signed in, you enter the 25-character code. The system validates the key and adds the subscription or license to your account. From that point forward, you no longer need the key itself to install the software; you simply sign in to your account on any compatible device. microsoft office 365 product key
The key follows a specific five-by-five format: . Its primary purpose is to validate that your software is genuine and to determine which plan you have (e.g., Personal, Family, or Business). Personal Key: Valid for one user across multiple devices. Microsoft has never sold "lifetime" Office 365 subscriptions