Launch System Preferences and in the General preference enable the Ask To Keep Changes When Closing Documents option. Close System Preferences. Launch the application you want to work with and do something. Save the document. Edit your document and add more content--delete some words and add a couple of paragraphs, for example. Choose File -> Duplicate (Shift-Command-S). You will now have two identical documents open. Close the original document. Because of the option you enabled in the General system preference you'll be offered the option to revert your changes, thus giving you a saved version of the original copy.

Fine, fine, another spittle break.

So, what we're after is a single command that invokes these steps: Duplicate, Close, and Revert Changes. AppleScript might be an option, but not all applications are scriptable (Preview, for example). I've solved the problem by turning to Stairways Software's $36 . This is a fine macro utility (remember those?) that allows you to trigger a gang of actions with a single keystroke.

Specifically, I created a macro that performs the following actions:

Type Shift-Command-S (to invoke Duplicate)