These tools read the key from the registry or UEFI without installing anything.
If you are not comfortable using Command Line, dedicated software is the easiest route. Warning: Many "key finders" on the internet are malware in disguise. Stick to this list.
What if your PC is "dead" (Blue Screen of Death or broken hard drive)?
You have two options:
This works for most pre-built PCs (Dell, HP, Lenovo, etc.).
Press Win + R , type powershell, and press Ctrl + Shift + Enter (runs as admin).
Copy and paste this command, then press Enter:
(Get-WmiObject -query 'select * from SoftwareLicensingService').OA3xOriginalProductKey
If a key appears, copy it exactly. If blank, your PC uses a Digital License (see Method 3).