According to Some basics on Android storage system it is not possible.
The Activity Starter enables you to call another app, here a pdf reader. The pdf reader app now must read a pdf file, which is stored in the ASD of another app (your app).
Just add a screenshot of an example project, which uses the activity starter to read a file from the ASD into this thread including aia file, so everyone can check… Thank you…
Taifun