I like the MuPDF Adnroid lib since it written in C++/NDK and it has unique features like clickable images (I mean an URL linked to the image) - met no other lib with this feature and I was really need it.
You actually can open PDF using no lib at all: using WebView via google docs but I don't like this way due to IC is required all the time while using MuPDF I can DL pdf file and freely open it offline any time. Also WebView way is more "hard" for device meaning battery draining + lags + CPU heating and it uses more trafic (if compared to DL&show way).
