The work is in the archives, not the application
The application is a form. Everything else is proving an unbroken chain: you, your parent, their parent, and so on back to the ancestor said to have been a Bulgarian citizen.
Every link requires a document. If one is missing, the chain does not close.
Where the chain breaks
Missing records. People born before the wars, during border changes, during migrations. The record may sit in another country’s archive, or may never have been issued in the form used today.
Name discrepancies. The same name spelled differently in three documents, having passed through different alphabets. This is the most common problem. It is resolvable, but it is a separate piece of work.
A broken branch. A relative for whom nothing survives, through whom the connection runs.
This often reaches municipal and state archives, and sometimes archives abroad.
Time
This is not a procedure measured in months. Gathering the documents takes a long time, and the proceedings themselves take longer still.
I will tell you that honestly at the start, rather than let you discover on your own that you are in something lasting years.
When I will tell you it is not worth it
If the connection exists only in family stories, with not a single document, and the ancestor comes from a region and period whose archives did not survive, the prospects are poor.
The first job is a preliminary check of what can actually be found, before you have invested money and hope.
Be careful with intermediaries
This field attracts promises. Nobody can guarantee an outcome in a procedure like this. If someone offers you a guarantee, that in itself tells you something.
Related
Reissuing foreign civil records, permanent residence.
What I will need
What you know about the ancestor: names, approximate years, the place, religion, the circumstances of leaving. Every document the family has kept, however old and illegible. Your own records and your parents’.
This page provides general information and does not constitute legal advice on any specific case. Rights and deadlines depend on the facts and the applicable law.