There’s plenty of apps to read, review, and mark up PDFs.
I find LiquidText particularly elegant. It’s the closest digital tool I’ve found that feels like I’m reading and writing on printed pages.
You can highlight and make annotations on LiquidText – but that’s not what makes it great. My favorite feature is how you can pull out selections, organize notes, and add comments in one place from multiple documents.
LiquidText is currently available on the iPad. It should be available for Microsoft within the year.