Portable Document Format or PDF files are great in keeping documents secured. That's because the texts on PDF files most of the time, can't be copied unlike word documents. Making it ideal for academic e-books, contracts, etc. However, due to the same reasons, some PDF files are hard to open on Android devices. 

Fortunately, this app will allow you to open them. It is an Offline Java PDF viewer for ANDROID. The app works on phones and tablets. It requires Android 1.5 and up. It has a simple interface and is very user-friendly. It is free to use and download. So, go get it today!