Assuming you found a source that claims the working file, follow this generic guide:

Below is a write-up detailing the game's actual requirements and how to safely access it. Assassin's Creed 1: PC Overview Assassin's Creed

: As the publisher, Ubisoft provides the game directly through its own launcher. Risks of "62MB Highly Compressed" Versions

Please note that downloading and installing games from unofficial sources may pose risks to your computer's security and violate copyright laws. This text is for educational purposes only.

Files that look like the game but install harmful software.