Not sure about PDFs, but the text for Dart Up & Running can be found here: https://www.dartlang.org/docs/dart-up-and-running/

[disclaimer: I work for the Dart team, and I'm a coauthor of that book.]

I usually browse the docs when starting with a new topic; the dartlang website has tons of stuff (and the articles are usually kept up to date), it's quite easy to get started.