You can install FortiClient on a Microsoft Windows Server 2008 R2, 2012, or 2012 R2 server. You can use the regular FortiClient Windows image for Server installations.
Refer to the Microsoft knowledge base for caveats on installing AV software in a server environment. See the Microsoft Anti-Virus exclusion list.
When installing FortiClient on a Microsoft Server, it is recommended to only install the mandatory Security Fabric Agent feature. Installing other features such as Anti Virus, Web Filter, and Application Firewall affects server performance, even if they are disabled.