Please refer to the following link (by the Ministry of Foreign Affairs, Bulgaria) to check whether you require a visa to enter the Republic of Bulgaria or not:
https://www.mfa.bg/uploads/files/VisaRegime_for_foreigners_ordinary_passports_en.pdf

In case you require a visa, then please contact the Bulgarian Embassy nearest to you. The contact information for the same can be obtained from the following link:
https://www.mfa.bg/en/pages/109/index.html

 

 

OTHER

Laissez-passer (OOН)

In cases of official trips the holders of a valid laissez-passer issued by the United Nations Organisation (UNO) are exempt from the requirement to possess a visa for transit passage and for short-term sojourn for a period of up to 90 days within 6 months starting from the date of the first entry.

Travel order (NATO)

In cases of official trips the holders of a valid official identification document or travel order issued within the North Atlantic Treaty Organisation (NATO) are exempt from the requirement to possess a visa for transit passage and for short-term sojourn for a period of up to 90 days within 6 months starting from the date of the first entry unless other provisions are stipulated in the international agreements under which the Republic of Bulgaria is a part.

 

Bulgarian Ministry of Foreign Affairs https://www.mfa.bg/