Not sure if I accidentally clicked wordpad as the open location for downloads but when I try to download a GTA mod, it'll say "Open with" and the default is wordpad. How do I get this back to normal where I can download the files correctly?

I'm new to PC gaming so naturally one of the first things I'm going to do is get GTA V and install some of these awesome mods I've been hearing about. However, how do I know there isn't any viruses in these files? I have a new computer and I'd rather be safe than sorry. Are viruses a regular thing in modding files, and what is a good way to determine what to install and what to stay away from?
Thanks.