I hadn't realised that what I'd written wouldn't be clear, because things like searching for and backing up save files is very normal to me! But I can definitely appreciate this sort of thing being unfamiliar.
You should never need to buy a second copy of the game on another account in case something goes wrong (unless you primarily want to support the game more), in that way digital media like this is different to physical media. Even if you did buy it twice on two accounts, if they both play on the same PC and the install files got corrupted you would probably find you cannot play with either account, since your computer would try and be smart and use the same single install rather than make two full separate installs.
In fact you hardly need to worry about corrupting game files at all, for example if you bought on steam if you think game files might be corrupted or acting weird, you can open game properties and there's a "verify integrity of game files" button. Simply clicking that will make the computer check all the game files, and reinstall any part it finds wrong. Another feature of steam is that it has the Steam Cloud synchronisation available for Planet Zoo, so if you have this enabled (I think it usually is by default) and you were to log in with your same account on another computer and install the game there, it would bring all your save files with you (I am not certain if all your blueprints would also come over, but it is highly likely).
When it comes to concerns about corrupting of save files, the safest thing is, as you say, a simple copy and paste. I think it's a smart idea in general to periodically make a copy of your save files especially for large, long-worked-on favourite zoos, that would be a great shame if some little bug corrupted the save and you lost it all. The game has been known to occasionally have bugs that corrupt a save, but if you have a copy from before that happened you should be able to delete the corrupted version and copy your previous one back into the folder with the other saves and rescue your work up to that point at least!
This kind of process for sharing and backing up saves varies a lot from game to game, and is not always this approachable especially for games that do not want you to cheat by duplicating save files which causes duplicating items collected or something similar, but in this game we are lucky that the files are relatively easy to find and make copies for backup or sharing whenever we want.
If discussing any of these things in more detail would be helpful I am happy to do so, some things I have written about may be too basic or too unfamiliar and it can be hard for me to gauge what details will be most relevant!