There's an almost 6 year old question about this (Two-page view in full screen for Adobe Acrobat) that I came across while searching for a solution.
In Acrobat Reader DC (version 2015.020.20042) on a Windows 10 machine.
I click on
View | Page Display | Two Page View
and the page look great. But the moment I click on full screen I have a single page filling up the middle of my screen with massive amounts of emptiness on both sides.
Thinking that the problem was the new reader, I uninstalled Acrobat Reader DC and installed (downgraded to?) Adobe Reader XI and still had the same problem. Two pages viewed nicely in "windowed" mode, but the moment I went to full screen I had only a single page showing at a time.
To summarize, I'm on Win 10, I've tried both ARDC and ARXI and both refuse to show 2 pages in full screen mode.
Does anyone have a solution to this? I swear that sometime in the past, I was able to view 2 pages in full screen mode.