Use Calibre,
https://calibre-ebook.com/ it has a built in ereader and it can convert epub to pdf. It's a very feature rich bit of software, meaning a learning curve, but there are plenty of sources of help for it, like here
https://www.mobileread.com/forums/forumdisplay.php?f=166
Decent ereaders for android are librera, readera, lithium and moon+reader. Some people like FBreader since it works cross platform.
Google is something to avoid. You must upload your books before the app opens them. Very annoying.