YoYo Games once released a Lite version of Game Maker 8.1 for free. The Lite version lacked many Pro features (DLLs, particle systems, texture pages, etc.). Some archival sites (like Internet Archive) host the Lite installer legally, but the Pro version remains copyrighted software.
Typing that phrase into Google or forums leads you down a dangerous path: license key for game maker 81 pro link
If you find a website offering a “direct link” to a license key or keygen for Game Maker 8.1 Pro, you are likely exposing yourself to: YoYo Games once released a Lite version of Game Maker 8
Game Maker 8.1 was built on outdated technology (Delphi, DirectX 9) and lacks modern security fixes, 64-bit exports, and current OS compatibility (Windows 10/11 often run it poorly). Game Maker 8
Short answer: No, not officially. YoYo Games no longer sells or supports Game Maker 8.1.
Longer answer: If you already purchased a license back in the day, you might be able to re-download the installer from your old YoYo Games account (if it still exists). However, even then, the Pro features may not unlock without offline authentication workarounds – which are not officially supported.