You can use Mondo to create a bootable ISO backup of an existing system:
http://www.mondorescue.org/
However, the existing system may have made choices for your physical hardware and not include what you want on your Hyper-V guest.
Here we simply download the original Linux ISOs for installation and load those on our Hyper-V hypervisors and do a new install when creating a new guest.
It sounds as if you're trying to migrate an existing physical to a guest and Mondo may work for that. Mondo does allow you to make changes on new hardware so can be used for moving to a newer physical system but I've not tried it for migrating to a new virtual guest.