If you want to stay entirely legal, the best path is: Buy the Steam version ($10), then download a from the Internet Archive that replaces the Steam exe with the 2004 version’s framework.
To play Sonic Adventure DX on the Internet Archive, follow these steps: sonic adventure dx internet archive
If you want to play SADX on PC the right way today: If you want to stay entirely legal, the
Original disc rips lack the restrictive DRM found in later digital storefront versions. Their mission is to preserve and make accessible
The Internet Archive (IA) is a non-profit digital library that provides universal access to cultural, historical, and educational content. Their mission is to preserve and make accessible digital artifacts from the past, present, and future. One of their initiatives is to emulate classic games, making them playable directly in web browsers.