Does Unity support stl files

Does Unity support stl files? I found an online model that I really want to use in my game.

No.
You can convert it into a .obj file using this.

As mentioned in an answer to this question, you can convert STL files to one of the supported formats, such as an .obj file.

No.

Please download the testing application first to check if your model can be loaded:
http://ricardoreis.net/trilib/trilibtest.zip

,@rickomax, if I can see the object in the Asset Loaded, it means I can import it in Unity?

Yes you can (I am using 2018.3.0b12)!