Open, Save and View PDF

Guys, I have a button that after clicking it leads me to a site where I download a file that is in PDF.
What I want is as soon as it is downloaded to my cell phone, get this same file, save it in Firebase and after saving visualize it.
I don’t know how to open this file after it’s downloaded on my phone and where to save it if it’s on Firebase Storage or RealTime database.
Can someone please help me?