I recently got a task to make a online document review app, which can basically work as microsoft word, with editing, proof. However, we don't have to expect it as good as MS word.
There are some products out there that carries the basic idea, like:

http://a.nnotate.com/
http://www.pleasetech.com/pleasereview.aspx

I am not sure which techniques I should use to work this out, javascript? php?

Currently, I work with Django, so I hope it could be something that can be integrated into Django (although this seems not to be a problem).

It will be great if there is any source code that I can play with. Even some codes of similar function will be great!
Thank you so much!