As mentioned, ISD and Unarc are not game files, they're Windows files. I'm pretty sure the first relates to Information Storage Devices, and the second relates to Archives. As also mentioned NEVER source missing OS files from some random site on the net. W10's SFC does plenty good enough job at scanning and repairing system files as long as the system image is healthy, which is what DISM is for.
Since they are both basic and necessary dlls for installing programs, games, etc, besides a SFC scan, you should also probably check for any possible malware or suspect 3rd party apps that may have corrupted them. Try checking for startups that don't need to be running as well, and look in Programs and Features for any installs that you are not...