[Silentio]

The only problem with digital copies like this is that I can't underline. Maybe it's just the habit of underlining, but I can't read as well (academic reading) when I can't underline key points, specific words, and particularly interesting passages.

[drewcrawford]

I've found Preview's (Mac; built in) annotate feature to be a great portable way to highlight inside PDFs.

[Silentio]

I agree that Preview's annotate feature works well. Still, there something about the physical process of underlining words that helps me connect ideas together as I'm reading.

[jimmyjim]

I may be wrong, but I believe there's a feature in Kinde 2 DX that allows you to do that.

[fortes]

Not sure about underlining, but highlighting and annotating has been there since Kindle 1.

[elq]

the DX cannot highlight or annotate pdf files, at least not currently.