What do I do with some files like: Choir - Omnia,Thrill,Contact Factory Library 2

I've recently bought Native Instruments Komplete 14 Collector's edition. I started downloading files were downloaded without any issues.However, there are some big files that I've downloaded (.iso files.) When opened, two files pop up: .exe archive file and .pkg installer file.

When I want to unpack archive, it tells me that Unarchiever cannot open that file. Is there a way to open it or download free application that can do it?

When I try to open .pkg file, window pops up and the message says: digital signature is not trusted.