Is there a native way of managing pdfs?

New to iPhone. And fighting with it, so it's likely something I'm not thinking in the way I should.

Let's see: I've PDF files on an old Nokia phone. I want to read them on my iPhone (saving them previously into its local 16GB memory). So I decided to send them by email to my gmail account. But when reading the mail on my iphone with either Safari or the gmail app, there's no way or saving the attachments into the iphone)

What am I thinking wrong? How should I proceed?

TIA