Where to find nRF9160DK hardware files (schematics, layouts)

Hello. I would like to learn more about nRF cellular module and how it works.

I was a little bit confused when I first received the development kit and noticed that there is weird microcontroller on the development board (MK22FN128VL110).

After reading the nRF9160D in the products section:

https://www.nordicsemi.com/Products/Development-hardware/nrf9160-dk

I could not find any information about this. I was under the impression that this board only houses nRF91 + nRF52840. Can someone help me understand what is the purpose of having additional MCU on the board?

Also, I was hoping to find hardware files so I can look into this more but there is no hardware files attached for the nRF9160DK. In the infocenter, it mentions that the hardware files can be found on product page:

but the only documents availble on the product page are the following:

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