The most legitimate way to activate Windows 7 without a product key is to purchase one from Microsoft or an authorized retailer. Other methods, such as using activators, come with significant risks.
These tools trick Windows into believing it has a genuine license, removing activation reminders and allowing full access to updates (though not always safely). windows 7 activator archive.org
Surprisingly, many Windows 7 OEM keys still activate via phone or online. You can find them on: The most legitimate way to activate Windows 7