Pc Gamer how to get achievements?

We all know that in some games there are hidden steam achievements, I mean the terms are hidden. Yes, you can look through the page of the store, but you can even find out just the name. So use steam achievment manager, even the secret achievements is the description of how to get them (at least I have not found without it). So why am I in this prog I have this game as a PC Gamer (Yes,as a curator in steam) in the steam library it of course not. However, Yes sometimes it is. What a miracle, and most importantly how it achievements to get?