I am using an iPad mini 4 for reading long PDF books with Acrobat and it works great, it's the best amongst other products. But there's one annoying thing happening: if you switch to another program (like Notes or Safari) and then switch back, it will render PDF at the same position vertically, but horizontally it will be at the left border instead of where it was. This gets annoying as you need to make many notes or look things up in web as you read. Hopefully, it's not hard to fix his. Thank you!