Do you mean..
Can you put Windows (Server 2012 r2 for example) on a sever as an Operating System and have all the other desktops in the office connect to the server for whatever it is doing (email, file share, printers, etc..)? Then yes, you can, that is the way is is supposed to work.
Or did you mean..
Can I put a desktop OS like Windows 8.1 on the server and not have to pay for a copy of Windows 8.1 for all the other machines in the office? Then No, sorry.
But there are some options. Talk to Microsoft about getting a license for you your business, and not just for operating systems, for MS Office too. Tell them what you want and they will be very happy to give you a price. Some options may make sense for you, some may not.