Keep an eye on http://hypothes.is http://hypothes.is. I think they plan to support private annotations, and handle PDFs through pdf.js. It doesn't have an offli

Keep an eye on http://hypothes.is http://hypothes.is. I think they plan to support private annotations, and handle PDFs through pdf.js. It doesn't have an offline document management component, but it could be used as the annotation component in a larger system.