I often have multiple Word files open as I'm working. The documents I'm not looking at are still available in tabs at the bottom of my screen (called a toolbar, I think), so I can just click on them and bring them right back up instead of going into my C drive and opening them all over again.

Yesterday, Word started closing the file I'm viewing if I open another. That is, it won't keep the original file open in a tab any longer. It just closes out or "replaces" my current file if I open a new one.

How do I fix this? I've tried searching "options" and the "help" menu to no avail.