Did you get the "Garmin maps" from Garmin? If so, they should have come with a program called MapSource on the CD/DVD. It should have been installed at the same time as the maps were installed. MapSource will let you view Garmin's maps and also any Garmin-compatible maps you get.
If these are Garmin-compatible maps that did not come from Garmin, you can install MapSource and it might let you look at them.
How to install MapSource to add maps to Mobile PC
If the maps came as a GMAPSUPP.IMG file, MapSource will not let you look at them. That is a compiled map file that will only be useful on a Garmin GPS device like a Nuvi or Zumo or eTrex, etc. It will also be viewable in Mobile PC.
There is an explanation of Garmin's maps in
Garmin Mobile PC - FAQ
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