This was my original question:
I want to be able to open a pdf file in my app using the android\'s built in pdf viewer app, but i dont know how to
Although this is a pretty old topic, here is a solution for opening a PDF that is in the asset/ folder with an external PDF reader app. It uses a custom content provider: https://github.com/commonsguy/cwac-provider
Using this you can define any file to be provided from the assets/ or res/raw/ folder.
Try it! Best and easiest solution I found so far.