Downloading unauthorized versions of Houdini poses several serious risks:
You get access to nearly all the features of the professional version, including advanced nodes for modeling, animation, and simulation.
Using the official build allows you to learn the software exactly as it's used in professional studios. How to Download Old Versions (Like Houdini 19)
If you are a student or a hobbyist, you can download for free from the Official SideFX Download Page .
If you specifically need Houdini 19 for a project or course, you can still get it officially: Create a free account on the SideFX website.