@H Williams
I've seen many old school buildings come on the market, and they are usually BIG and a TON OF WORK. I'm pretty sure it would cost you a small fortune to renovate. It's true that I'm lazy and risk-(and work-) averse, but I suggest you think this through very carefully before you go for such a bargain!
Like most places, Bulgaria does categorize property based on use. The difference, I suspect, is that Bulgaria is often not very aggressive on enforcement. For example, there are many, many, small shops and offices (and even garages) which have been converted to apartments, and I doubt anybody cares. If you were to acquire a former school in a small country village, I would be very surprised if anyone objected to you renovating it, or living in it while (or after) renovating.
Changing the status is a possible, but a bureaucratic hassle (probably) requiring time and money (and professional assistance) to accomplish. I own a small property in downtown Plovdiv, which was shown on the Notary Act as a shop ("magazin"). It was actually being used as an office, with no issues. I started a renovation to an apartment, as one of them fancy live/work spaces, and I doubt it would have been a problem. However, being a well-behaved and worried foreigner (knowing how not allowed this would be back in the UK, say) I did pay someone to do a change of status application (to atelier, a versatile shop/office/apartment designation). It took a couple of years to come though, but didn't involve any great drama.
Act 14/16 are certificates related to the construction stage of the building, rather than the specific zoning of a particular unit. Roughly, Act 16 means that the building is recognized as finished (even though, thanks to Bulgarian Standard, it really isn't). You should avoid any property that doesn't have its Act 16.
One of the disadvantages of commercial/shop designation is that electricity and water is charged at much higher commercial rates.
If you really love the property and are determined to press ahead, I suggest you at least pay for a consultation with a local attorney to cover these issues. (I can recommend one, just private message me.)
