If well is true than can hide it using Shift+F4 or click at the arrow next to that panel, when you open attached PDFs this panel opens again
I hope you are doing well. I am sorry for your experience with Acrobat Reader.
Generally, whenever you open any file, the panel for the tools does open up automatically so that you know the panels you use to work.
However, if you do find any irregularities with the panel showing up, you can try resetting the application's preferences to the default and check.
You can view the below link to learn more on how to reset:
Hope this helps.