Where can I find the paperui html files?

Where are the paperui files located? I just found this repository from an older discussion. There is this file for example. Where is this file located in the openhab2-master folder?

I just would like to start with little changes to this ui. Furthermore, are there any tutorials to get access on the ui? Or how to edit content of this ui and how is it connected to the openHAB code?

It is currently located here, but in the process of being moved to ESH.
New contributors are in general very welcome on it (as there are still million things to work on), but as the codebase is currently under IP review by the Eclipse Foundation, I would suggest waiting until the PR on ESH is merged - then the code will be actively maintained there.

In my packages of openHAB2 and ESH the partials folder of the uis aren’t available. How do I create my own extensions via the include.extension.html and js/extension.js?

Another question is, how to import the paperui from your link in my openHAB2 IDE setup?

Solved, I had to run bower install in the extensions\ui\org.eclipse.smarthome.ui.paperui folder as described here.