Microsoft no longer forces you to dig up an old sticker. If your PC has ever had Windows 10 Pro activated on it before, you likely have a (also called Digital Entitlement).
The short answer is: Windows requires a valid license to remove restrictions. how to activate my windows 10 pro without product key
You must purchase one from Microsoft or an authorized retailer (e.g., Amazon, Newegg). Home users often find cheap OEM keys, but be wary of "too good to be true" pricing. Microsoft no longer forces you to dig up an old sticker
If you have a previous version of Windows activated on your computer, you might be able to upgrade to Windows 10 Pro without a product key. how to activate my windows 10 pro without product key