According to several comments, it was possible to use the demo in order to access the full game. We won't touch on the specifics of the process here; it's a moot point anyway as the demo has been taken down, and an update has been released rendering the demo unplayable for those who had it. If you did download it, and want to play it some more (without using any weird bypasses...), you should start Steam in offline mode and play it without updating.
While some game demos are separate entities entirely, a number of them are simply the full game with a software lock in place to prevent the player from progressing past a certain point in the game or playing beyond a pre-allotted time. In this case, the pirates were able to circumvent the Denuvo DRM on the demo and then copy over files obtained in another method to that area to play the entire game
The Trials of Mana demo has been temporarily taken offline following a reported exploit that allowed dishonest individuals to access the entire game. Trials of Mana is the 3D remake of Seiken Densetsu 3, the third game in the Secret of Mana series which never made its way to the West. It was...