Is Page Setup Shared?

In a shared environment, is this applied on a client by client basis, or does a change affect all clients? My need is to make it local.

Yes to both.

When you change the page setup, that setup information is kept in the local copy of the file. So each client can have a different page setup.

However, if you do a new sharing generation and choose the Field Arrangement and Data Types option, then the entire database is uploaded to the server. This includes the page setup information. So in that case, the database on all the clients will be set to whatever the settings were on the uploaded copy.