Tariq Dar • Adobe Employee, Feb 12, 2021Feb 12, 2021
Thank you for reaching out. Adding to what @gary_sc said. Now with the latest release of Adobe Acorbat Pro DC you can dock it by clicking the icon on the far right on the screenshot you have attached.
Let us know if that answers your question.~Tariq
That's a HUD (Heads Up Display). It appears when you are looking at a pdf in a browser. If you want it to do away, move your cursor off the screen and/or away from the region of the HUD. Also note you can move it around by clicking and dragging it around.
But you cannot get rid of it, those are your controls for PDFs in Browsers.