Check the driver’s authority to take the vehicle abroad, the registration details and insurance coverage for every destination. A rental contract alone may not authorise travel into Bulgaria or onward countries. Company vehicles may need authorisation records, while privately borrowed vehicles may require owner consent or an appropriate power of attorney. Confirm document format, translation and certification requirements for the specific circumstances. Ask the insurer about territorial coverage and the rental company about cross-border conditions. Customs and road rules need separate checks, and medical insurance does not replace motor insurance.