When you are reading a long document, it's often necessary to jump around in that document. Getting back to where you were previously is difficult.

Furthermore when you are on a tablet device, it's VERY EASY to flip the page marker or scroll uncontrollably and accidentally move to some completely random place in the document! Oh the number of times I have done this! It's so frustrating!

Suggestion: Add back and forward arrow buttons like in a web browser. Save the place in the document each time the location changes. Each page change and each large jump. For long periods of scrolling, mark only where the user stopped for more than a few seconds.

This will make it much easier to recover from "oops" mistakes and also make it much easier to go look in another part of a document and not have to worry about getting back to where you were to continue reading without having to try and remember to manually book mark where you were.