windows to imac

If its an Intel Mac, you can install a number of VMs like Parallels, Virtual Box, VMware etc... and can install and run Windows on the Mac in a windowed Virtual Machine.

You can also if this is an Intel iMac install Windows on a partition and boot to it directly using Bootcamp.

click here ➜ Install Windows 10 with Boot Camp - Apple Support

You would need a valid Windows Installer and key for either of these.

With Windows installed with either of the above methods, you can then run any Windows App you want directly.

Outside of that, there does not appear to be any App for Mac that can directly open the cd3 file type.

What application are these cd3 files used with on Windows exactly? The extension does not identify a particular format directly so its hard to provide any suggestion without knowing what they are for.