I had an issue at a client’s site today where they have a MacBook Pro running macOS Mojave 10.14.5 and Adobe Acrobat Reader DC.

What would happen is that when you opened a PDF in Acrobat, it would come up on the laptop’s internal display. As soon as you try to drag it to the external display, Acrobat would crash. 100%. Every. Single. Time.

I was able to find a fix on the Adobe forums:
https://forums.adobe.com/message/10728993#10728993

It was slightly more complicated than the answer given in that when I right-clicked on the Acrobat icon in the Dock, I didn’t get the option to assign it to desktops on any particular display.

What I had to do was drag the Acrobat windows up to the top of the screen, and keep dragging upwards. I then put it on it’s own display. Once I had created another display, I then had the option to assign Acrobat to the Desktop on Display 1.

It immediately crashed after I did this, but upon relaunching it, it came up on the external monitor and, so far at least, it seems to be happy now to have windows dragged from one display to the other.