Work folders in DC 2008 R2

We have Windows 2008 R2 environment and the DC's are at Domain functional level of Windows server 2008R2. Can we install Windows 2012R2 file server (not DC) and test work folders or we have to add Windows server 2012R2 and promote it to a DC and raise the functional level to Windows 2012R2 in this environment of Windows 2008R2 then install  a Windows 2012R2 file server for work folders.