It's a tool for reading research papers (PDFs) together with your colleagues. You can read, annotate, comment etc.
Needless to say, it led me down quite deep into the PDF world and it.. was interesting.
As far as I know, PDF/A is the only format that fits the first two specs. I know annotations are in the PDF specs but is it reasonable to think that annotations I make today will be readable - and updatable - in (e.g.,) 30 years?
The PDF 2.0 standard removed some parts of PDF 1.7, like the proprietary XFA forms. But most things stayed in PDF 2.0 and one can expect that those annotations will also be available in future iterations of the PDF specification.
And generally, since future PDF viewers will need to be able to view older documents (think: all the (signed) documents created by governments), you can expect PDFs created today to be usable in 30 years and more.