SQL Server Transaction Replication on different versions of Windows Currently we use SQL Server 2014 Transaction Replication in Windows Server 2012 (both Publisher and Subscriber are on different servers with the same operating system). 

We need to add a new subscriber, and my question is this: do we need to have the same operating system for the newly added subscriber, i.e. Windows Server 2012, or can I use the Windows 7 operating system.

Note : Both Publisher and Subscriber are in two different domains.
You can use SQL Server replication on different Windows versions.  What is more important is the version of SQL Server.

https://blogs.msdn.microsoft.com/repltalk/2016/08/12/suppported-sql-server-versions-in-replication-topology/