Similar to English, Bulgarian uses active voice (focus on who does the action) and passive voice (focus on what gets done). Look at the following examples:
Оставям ключа на масата. (I leave the key on the table.)
Ключът е оставен на масата. (The key is left on the table.)
We usually need the verbs for past completed actions (казах, направих, донесох, etc.) to form this type of phrases. Here are some examples:
Написах договора на български. (I wrote the contract in Bulgarian.)
Договорът е написан на български. (The contract is written in Bulgarian.)
Реших проблема. (I solved the problem.)
Проблемът е решен. (The problem is solved.)
Върнах продукта.(I returned the product.)
Продуктът е върнат.(The product is returned.)
Also, the forms написан, решен, върнат function like adjectives and change into написана/написано/написани, решена/решено/решени, върната/върнато/върнати based on the noun’s gender. Here are some examples:
Masculine: Ресторантът за сватбата вече е избран. (The restaurant for the wedding is already chosen.)
Feminine: Датата все още не е избрана. (The date is not chosen yet.)
Neuter: Менюто вече е избрано. (The menu is already chosen.)
Plural: Дрехите са избрани. (The clothes are chosen.)