Upvote:1
As Armenia is not an EU country, Armenian citizens do not automatically have the same rights as EU citizens.
Bulgaria is outside the Schengen area but they say they allow visa-free travel for holders of a Schengen visa.
I'd be surprised if Bulgaria considered a Polish work-permit to be equivalent to a Schengen visa. However I don't really know.
I'd expect an Armenian citizen to need a valid passport and visa to enter Bulgaria.
According to Wikipedia, for Armenians travelling to Bulgaria.
Visa not required for a maximum stay of 90 days within 180 days for valid visa holders or residents of the European Union member states
The EU say
If you have a valid residence permit from one of those Schengen countries, it is equivalent to a visa.
I'd guess a work permit is not an acceptable alternative to a residence permit and therefore insufficient evidence to prove you are a resident of the EU - but I may be wrong.
I think your plan of contacting the Bulgarian embassy well in advance of travel is best.