Then usually after signing that you can get the mortgage (at the very least it is much easier if bank gets the papers showing you're in progress of buying home).

After you sign the final deal, you pay and you are then written down (and bank, if you buy with mortgage) into land and mortgage register (which in my language is just called "perpetual book", funnily enough).

There is a bit more complexity when buying some old stuff that might not have entry in the registry, like my grand-grandfather house only have some documents for getting land from government after war and then them giving it to grandchildren few decades ago