Domain Join Template active-directory-new-domain

I saw the domain join template I am unable to understand why are we using the file
vnet-with-dns-server.json to update the vnet. The link of the files is
azure-quickstart-templates/active-directory-new-domain/vnet-with-dns-server.json

Start by reading the active-directory-new-domain template and vnet-with-dns-server.json linked in the issue. Trace how the file is used to update the virtual network, then document its purpose and make the relationship clear to readers of the template.

Written by the indexing model from the issue text.