Sometimes a document is so secret that once locked away, it can only be viewed once a deputy have unlocked it.  An example of this would be something like your grandma's secret cake recipe, or the codes to a nuclear warhead.

To mark a file as secret, find it in the file explorer and click the file.  Once the details have popped up, click Mark secret:

The details will close.  If you try to reopen, you will get the following warning:

If you click Request to unlock, your deputies will receive a notification of the request.  Their screen will look like this:

Only one deputy is required to unlock the file, so once one of your deputies have done this, the file is available to be opened.