You can also purchase and download it directly through the official Ubisoft Store or access it via a Ubisoft+ subscription.

This is the most reliable source. The GOG version is DRM-free and pre-patched to work on newer versions of Windows.

If you download the game, you will likely need a few community patches to fix issues like widescreen support or broken textures:

This is the most recommended mod for adding widescreen support and various quality-of-life improvements.