Hey, I wanna start developing Android apps. I'm good at java, I just need to learn how to use to make Android apps. So I looks for the books I need to read on Stack Overflow and some other sources. so now I have a bunch of different books that I don't know what book to read first. I just need someone who is experienced in mobile development to recommend for me what books or tutorials I need to go through first knowing that I already know java (for native apps) and html5 (for hyprid apps).
Thank you in advance.

Honestly picking up Android development was easy with a java background, it's how I sent my job (made an app that could send emails as a prototype for the job) if you just start with a simple tutorial it should let you head off in the right direction.

In terms of where exactly to start I'm not so sure lol, I just picked up the work app and went with it, though if you had a plan in mind of what you want just google the feature and you should get something.

I'll tell you now though that PDF viewing within an Android app will either make you waste time (looking for a 3rd party library) or money (buying something that works) I'd recommend against it lol.

Same with PDF creation, though Android pdfbox does do the job (a bit slow but 10 seconds isn't so bad, for a free library lol)