Which documents do I need to prepare for handover?

Short answer

Notify the client in writing that the works are complete.
The technical inspector confirms to the client whether the conditions for acceptance are met.
The client appoints the acceptance-at-completion commission within 3 days of that confirmation.
Hand over the construction technical logbook, compiled during execution, together with the specialist reports from the designer and the technical inspector.
Once the warranty period expires, the owner organises final acceptance, setting the date within 10 days of expiry.

The construction acceptance regulation (Government Decision 273/1994, as amended by Government Decision 343/2017) — acceptance happens in two stages: acceptance at completion of works, and final acceptance after the warranty period expires.
Law 10/1995 on construction quality — the warranty period is at least 5 years for buildings in importance categories A and B, 3 years for category C and 1 year for category D.
Law 50/1991 on authorising construction works — completion must be notified to the authority that issued the permit and to the State Construction Inspectorate, and the fees regularised.
State Construction Inspectorate Order 1370/2014 — the protocols from key inspection milestones, notified to the territorial inspectorate at least 3 working days in advance, form part of the documentation presented to the commission.

Example: for an office building in importance category C, acceptance at completion happens in June, the warranty period is 3 years, and final acceptance is scheduled three years later, with the date set within 10 days of the warranty expiring.
Example: the file presented to the commission contains the building permit, the site handover protocol, the key-milestone inspection protocols, the designer's and technical inspector's specialist reports, declarations of performance for the products used, and the as-built documentation. One missing protocol postpones acceptance by weeks.

Starting to gather the documents at the end of the job, even though they are produced throughout execution.
Not compiling the technical logbook as you go; reconstructing it retroactively is the most common reason acceptance slips.
Missing the key-milestone inspection protocols, which cannot be recreated once the work has been covered up.
Treating acceptance at completion as the finish line and never scheduling final acceptance after the warranty.

Documents are attached to the stage that produced them, during execution, not to a folder assembled at the end.
The daily journal keeps photos and stage sign-offs with their dates, so the evidence of execution exists at handover.
Every project carries a full history of confirmed stages and work statements, useful to the acceptance commission.
The warranty expiry date stays tracked on the project, so final acceptance isn't forgotten.