[Today]. When you scan, the variable will reflect 'today's date'. If you want the date presented in a different format, double-click in the value (right) side of the IDB screen. The variable will be saved with the other values in the IDB record.

[-Today-]

 

If you type the word 'Today' and press Alt-G immediately afterward, it will give you a choice to replace the word with the 'static' date or to replace the Word with a field that will change every time you open the document. (In the latter case, you will not preserve when the letter was composed or sent.)