If you have an older version of the game, you need to get all the updates first. Trying to use it with older versions or “cracked” versions of the game are not currently supported so there’s a chance this program won’t work. It’s designed to be compatible with the latest official Steam version of Dark Souls 3. This software is an Injection DLL Library that makes it much easier to install mods so there are less mistakes, less confusion and helps remove the risk of a ban. The Mod Engine is the program you need to download from Nexus Mods to start installing mods to use. It would stop you from playing with others online.
Warning: Because modding is not supported by the developer, installing mods can result in a ban if you try to play the game online.