When using Microsoft Word 365 I can sometimes open two instances of the same document.
View > New Window
These are both live views of the same document. i.e. when making changes on one window, they are immediately visible in the other window.
Sometimes 'new window' is greyed out and I cannot replicate this feature by trying to open a second copy of the doc through other means. I have tried right clicking on the document in the recent items list, taskbar and the file in its folder. These just seem to reload the existing file.
I think that the fault is document specific. i.e. I currently have two documents open and in one New Window works and the other it does not.
I have tried disabling macros to see if this would fix and it did not (at least when I change security settings to disable with notification, reloading the doc does not fix the greyed out option).