Hi Roman,
I'm glad to hear you're going to visit our amazing country this month 😉
In fact, it's mandatory.
The law obliges me, as host of local accommodation establishment, to report to the Aliens and Borders Service (SEF), within three working days of entry and within three working days of departure, the stay of foreign citizens in the accommodation. The information we must provide is: name, surname, date of birthday and passport or ID number.
In my particular case, I send a bulletin by e-mail (15 and 2 days before the check-in) for the guest to fill in this information. In case it hasn't been covered before the check-in, I ask to take a picture of the passports and I do it by myself at the office. Otherwise, we do it together in the check-in.
Hope to have clarified your doubt.
Cheers,
Luis