Multiple users accessing document on network share

In our small office we have a couple of numbers douments that are regulary accessed and updated by 3 different people on three different machines, the numbers documents they access are stored on a network share on the Mac Server in the office.

The problem we have is that all three able to open a file at the same time, obviously this is causing all sorts of isues. People losing data they have put into the file and also causes issues with someone being unable to save the file while someone else has it open.

Surely there must be some sort of feature that when one person has the file open, its is locked for editing to everybody else that attempts to access it, I have searched around but cant seem to find anything to solve the problem. Anybody here have any suggestions?

Thanks

Craig