Visit a legitimate OEM key reseller. Pay $20-30 for a legal Windows 10 Pro key. Enter it in Settings > Update & Security > Activation.

The smart choice is to install the official, unactivated version from Microsoft. Live with the watermark for a week while you save $20 for an OEM key. Your future self—with clean credit and a fast, secure PC—will thank you.

However, the modern reality is harsh: Every single one of these files that exists on public torrent sites, forums, or file lockers has passed through the hands of someone with malicious intent. By installing one, you are not "sticking it to Microsoft"; you are surrendering your banking credentials, email logins, and private photos to identity thieves.

Boot from the USB drive and install Windows 10 Pro. When prompted for a key, click "I don't have a product key."

Choose "ISO file" to save it to your hard drive (or USB).