why does the bookmark side bar overlaps the main file and does not remain stagnant

when i open any pdf and click on the book mark icon, The Bookmark side bar overlaps the main file and keeps disappearing on my galaxy Tab7+. the same should appear and work like it works on my mac when its stagnant . so i can jump to any book mark when i want. otherwise i have to open the bookmark tab again and again and its very irritating, anyone has solution for this