There are two ways of inserting the date in a Word doc. One way will always update to "now" when you open or print, the other will keep the date when you wrote the letter.
If you have the date in the template that opens the document, it will always be the "update to now" version. I don't know of any way round that, although there may be one.
I use the "proper date" function. Here (no extra charge!) is the macro in my copy of Word, that does that:
Sub MAIN()
'
' InsertProperDate.MAIN Macro
' Macro recorded 16/05/99 by Keef
'
Selection.InsertDateTime DateTimeFormat:="d MMMM, yyyy", InsertAsField:= _
False
End Sub
Add that, as a Macro, then create a button on your toolbar to call it, and use that to insert the date when typing.
There may well be an easier way, but that one has worked for me since 1999 so I've seen no reason to change it.