What does this sound like? - To me, sounds like legal review. And indeed, you can get a free account, upload your PDF or Word documents, and redact it to your heart's content.
You can also have some business license, with groups, security, and privileges, and, what's more, you can do your own application using their API - although this is still shaping. I think they have done the redacting part just right!
What is the history and popularity of the application?
Founded by three MIT graduates, and one MIT attendee who dropped out in order to help launch successful internet startups, Crocodoc's creators are the same people who brought WebNotes, a tool used by professionals and educators across the globe to manage research, to the web. Y Combinator, and other investors provide funding for Crocodoc. The company is based in Silicon Valley California, and also has offices in Boston... (from this review)
Art: Paul Cezanne - Uncle Dominique As A Lawyer