Can I use Windows server 2012 and Ubuntu LTS 14.04 server in a single machine?

You can use different virtualization tools to do this. Depending on your specific Windows license, you might use Hyper-V to run Ubuntu, or you run both inside a VM on e.g. ESXi or KVM or countless other approaches.

However, doing this might be a bad idea, depending on even more factors like the hardware used and the use case, especially that of your Windows Server – using an AD DC as Hyper-V host is generally considered a very bad idea.