Automatic scrolling backwards/forwards. Screen freezes/goes black

Hello. I wish to thank everyone/anyone for helping me with this problem in advance. I have a Samsung Galaxy Note 10.1 Tablet (2012). I download books/articles onto my tablet using MoonReader+. For a few months now, I have been experiencing episodes when all of a sudden the screen will start going forward and/or backward quite quickly without any reason. It will also freeze when I am trying to highlight sentences--meaning the highlighting process freezes. My S pen does not seem to operate smoothly now also, which it did at first. I tried using a stylus with a rubber tip and it did the same thing. Additionally, sometimes the screen will go black for a few minutes then revert back to the regular screen. Someone conveyed to me that maybe the digitizer or touch screen might be the problem. When I looked up what a digitizer does--it didn't seem to my uneducated brain that that may not be the problem. I really would appreciate some help with this as the tablet was not an inexpensive one and I really want to use it. Again, thank you for your help.