After digging around, there seems to be a solution to remove that side panel that takes up screen space, every time you start Adobe Reader DC.
[you have to have admin rights to do this]
Go to the install directory using explorer.
C:\Program Files (x86)\Adobe\Acrobat Reader\DC\Reader\AcroApp\ENU
( If you have another language, go to another directory there, in my case “NLD”)
Create a new subfolder to move files to and move 3 files from the “ENU” folder into the newly created folder:
AppCenter_R.aapp Home.aapp Viewer.aapp
Open a PDF file and now there should be no tools panel.
Works with Windows10
Hope this helps you.