My great great grandfather is commonly known in my family to have been adopted, any work on genealogy completely stops there. What would the process of adoption have been like in the Austro-Hungarian Empire? How would it have been done? Who would it have been done through? Is there any possibilities of finding records of his adoption?
Well... unfortunately this would in all likelyhood be part of a Hungarian post-Ausgleich law, meaning it's written in Hungarian and thus illegible to the rest of the world. I could look up stuff of the Austrian half without issues but I don't speak a word of Hungarian.
If you're looking for genealogical information I suppose your best bet would be to contact Hungarian resources or researchers directly. They have great archives but most of them are paper only so incredibly tedious to look through even if you know where the hell you look for it.