Maybe I'm just being stupid but when I open the folder there is a file titled Procedural Level Generator.Unity.Editor. That might not actually be the editor, I'm new to Unity.
Viewing post in Edgar PRO - Unity Procedural Level Generator comments
It is not required to open any such file. You download the .unitypackage file, import that into a Unity project and after doing that, all the funcionality of the tool should be available in your project. The gui of this tool is compatible with the Unity editor. That means that you do not have to open any dedicated file to access the editor gui of this tool. I would suggest to read some Unity basics tutorial if you are new to Unity.