Many of these are cracked libraries ripped from paid commercial collections. Aside from the obvious ethical (and legal) issues, they are notorious for crashing Pro100 mid-project. Nothing hurts worse than losing a custom cabinet layout because a corrupt *.stl file bricked your session.
Disclaimer: This post is for educational purposes. Always respect software licensing agreements. Pro100 is a trademark of its respective owner. pro100 library download
But where do you find these files? And what does that mysterious “Pro100 library download” search actually turn up? Many of these are cracked libraries ripped from