PDFab - a default PDF viewer app based on DonManfred's PDFium wrap
I wanted a freeware pdf viewer without ads, tracking, data collection, and what have you. Besides, it wasn't obvious (to me at least) how to make an app that would be offered as default to open a certain type of file, especially a PDF. Time for some R&D fun, and here you go. Prerequisites...
www.b4x.com