Recombine tabs together into one window in Acrobat Pro

I have an end user who is using Acrobat Pro and they have tabs when they open up multiple PDF files along the top of the application.

They have multiple screens so they will sometimes drag one tab over into a second screen to get two windows of Adobe running so they can look at both PDFs at the same time. Easy and simple so far.

The issue is that they cannot drag an open PDF in a Tab back into another instance of the application. They are expecting the behavior similar to something like Google Chrome where you can have multiple windows open and then drag tabs over to recombine your windows. Is there some setting somewhere that I am missing or some feature that I need to make sure is turned on?

They state that they have Adobe at home and they are getting the expected behavior, but on the work PC they are not.

Any assistance would be greatly appreciated.