The legal situation is nuanced but clear. Microsoft allows anyone to download Windows 10 ISO files for free from its official website. However, downloading a "pre-activated" version is a different matter entirely. While downloading an ISO from a third-party site is not inherently illegal, the problem arises when that ISO has been altered to circumvent Microsoft's licensing — known as cracking — or if you use an illegally obtained product key. Using Windows without proper activation is possible, but using a cracked version or an illegal key is against Microsoft's licensing terms and carries legal risks.
Unauthorized ISOs are a prime vector for delivering malware. Hackers often inject malicious code into the installer, such as: Windows 10 Pro 64 Bit Pre Activated Iso Download