I am an Indian passport holder. I live in Amsterdam and have Dutch resident permit which allows me to travel through Schengen countries.
Do I need a visa for visiting Bulgaria (Sofia) for 2-3 days?
Indian embassy in Bulgaria says this
Holder of valid long term visas or residence permits issued by Schengen Countries are allowed multiple entries and a period of stay in Bulgaria for up to 90 days in any six-month period from the date of the first entry.
According to Timatic, the database used by airlines based on live information from national governments:
Visa required, except for passengers with a residence permit issued by Netherlands for a maximum stay of 90 days
So you do not need a visa - you just present your passport and residence permit card.
According to this document, you can enter Bulgaria without the visa. I would also call Bulgarian embassy to be sure.