Converting VHD files to VHDX

On Windows Server 2016, the default format is VHDX and VHDX provides lots of features and enhancements compared to its previous version.
That is not to say that VHD files have gone away, you might be migrating from an older version of Hyper-V, for example Windows 2008 R2.
or you might still be using VHD files because Microsoft Azure only supports VHD files and
you want to maintain a level of mobility between your on-premises infrastructure and
Microsoft Azure.