I've been searching for a simple way to see if and when someone has read or downloaded a document or file I sent. Binder is a simple, cheap and effective solution. It also notifies me by mail when the document is read and keeps an access log.

There are a few minor restrictions: (1) Limited file types, such as no zip or Markdown files (obviously with no page-level statistics), (2) No access to the reader's IP address, and (3) I would like to bind a group to specific authorized email addresses (also to be logged)!

Apart from that (that the authors could easily improve), my experience is extremely positive.

P.S. Adding a viewer for.zip and.md files is nice, but a simpler solution would be to show a generic image for any unsupported file type and let the user download it. In this way you will allow any kind of file. Another important feature, easy to to implement, is displaying the file checksum, such as SHA-256, to ensure document integrity (specially in approval).