Go to Tools – Options – Environment – Documents, and check the Reuse current document window, if saved option to give it a try.

Reuse Current Document Window option

If the current document window is dirty (meaning you’ve made a modification, but haven’t saved yet), the next document will open in its own document window.  However, if the current document is saved, then the new document will just open over it.

I tried using this from time to time when I owned testing it, but it wasn’t for me. 

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