What documents are required when purchasing?

The building permit should already be of interest: for example, if you buy an attic converted into living space (and pay accordingly), but the attic is not allowed to be used for that purpose, it could become problematic.

We are buying a completely normal single-family house, background property. The seller says he has all the documents, which company built it, etc. The house has been standing for 20 years. Should I really be concerned about the building permit? I pointed out the energy certificate to him. I don't actually need it, but it seems to be important. I have also requested written proof of a crossing right for the foreground property.