Q: how do i open a new page (new document) without closing existing one?

In the current version of Pages on a Mac you simply go to the File menu and Click New or use the keyboard command N.

I believe in Sierra Apps are supposed to be able to be Tabbed just like Finder and Safari, but haven't tested either Pages 6 or Sierra to see how or even if that works as advertised.

Peter

To get tabs, just go to Window > Merge All Windows. Windows in tabs even works in Pages 4.3.

Once you have done that does it make any consequent documents in new tabs?

Peter

Not in either Pages 4.3 or 6 when I just tested it. I thought it did when I tried it a couple of days ago, but maybe not. It's not a feature I'm likely to use much.

One thing I discovered that I like is that merging all windows only merged visible windows & did not include windows that were minimized.