After the Wikileaks scandal, the Department of Defense is using a new software that generates fake documents that send an alert when they are opened. This would allow the DoD to provide misinformation but also to potentially see who opened the file and where they are.
Unfortuneatly, there seems to be a few ways around this techonlogy. You can disconnect your computer from the Internet before you open files, but this can be averted by requireing the document to authenticate and alert before the contents are visible to the user. Once you have access to the contents, you could easily take screenshots of the information and delete the original.
For more info, see: http://www.schneier.com/blog/archives/2011/11/fake_documents.html