I advocate Acrobat.com to all my clients as a way of storing, sharing and collaborating on content. Most are not experienced in IT so they struggle with some basics that us IT folks take for granted. 

"Why do I have to send an email to let my colleague read the document"? is a common one.

So indeed, why not be able to give your colleagues read-only access to some or all of your files if you want their views? Well, because they might want to change the content and they do that in their own space. So why not use the Acrobat Reader approach and let them put sticky comments on it for you to edit, delete or accept as you see fit without creating multiple temporary documents in other file systems?

I can understand that I might have multiple clients files in my file space and I don't want one colleague or client to see stuff that's not for them, so that takes us into the ACL space, which might imply using a sledgehammer where one isn't needed. Perhaps a simpler, two-level authentica