How do I turn OFF the side tool bar?
What more do You need to know? How do I turn OFF the side (right side) tool bar?
In Acrobat :
1) Launch any PDF and collapse the RHP using the vertical collapse strip(with small triangle icon)
2) Close acrobat and relaunch any file ---> RHP will appear collapse for every further session
Please Check for the Latest Available Updates of Acrobat DC using Help -> Check for Updates.
Let me know if that doesnt solve the issue for you ?