The library you downloaded is not COM-based or a >NET library. It's a standard C-type library with only functions in it.
You cannot add a reference to it.
You can, however, call the functions in that library using P/Invoke. This requires that you know the exact names of the functions and the exact list of parameters each of those functions expects. There is no tool that will tell you these things. You MUST Have the documentation on the library in order to use it.
P/Invoke[
^]