Adobe stuffs it with all sorts of crap I do not want in an attempt to sell their online services, but the program starts up reasonably fast despite being bloated. There's just one important annoyance that the preferences can't fix: the Tools pane. It wastes the right side of the screen for a bunch of functions which I never use. It can be hidden, but there's no option to hide it permanently, so it has to be hidden again every time I open a document.
The Tools pane can be disabled by moving or deleting the
Viewer.aappplugin which creates it. For me, it is located at
C:\Program Files\Adobe\Acrobat Reader DC\Reader\AcroApp\ENU\Viewer.aapp. In 64-bit windows it would be in
C:\Program Files (x86)\, and the ENU part could be different if you have a different language installed. I created a new folder within ENU and put the file there, so I can move it back if I ever actually need it or if updates break because it's not there. It may be necessary to repeat this procedure after every Reader update.