Dave,

Yep to both.

Charlie,

Let's say you have four formfields  bookmarked Day Suffix Month Year

Laid out like:  effective the Day Suffix of Month, Year.

The Suffix field is not enabled for fillin.

You have another field bookmarked "FinalDate" that is also not enabled for
fillin.

One exit from the Day field you could run something like:
Sub MakeSuffix()
Dim oFF As Word.FormFields
Set oFF = ActiveDocument.FormFields
If Not IsNumeric(oFF("Day").Result) Or oFF("Day").Result > 31 Or
oFF("Day").Result < 1 Then
 'Handle your error
End If
Select Case oFF("Day").Result
 Case Is = 1, 21, 31
   oFF("Suffix").Result = "st"
 Case Is = 2, 22
   oFF("Suffix").Result = "nd"
 Case Is = 3, 23
   oFF("Suffix").Result = "rd"
 Case Else
   oFF("Suffix").Result = "th"
End Select
End Sub

On exit from the Year field run something like:

Sub DateAddUp()
Dim InputDate As Date
Dim IDate As Date
Dim FinalDate As Date
Dim oFF As Word.FormFields
Dim myString As String
Set oFF = ActiveDocument.FormFields
myString = oFF("Day").Result & "/" & oFF("Month").Result & "/" &
oFF("Year").Result
InputDate = myString
IDate = DateAdd("yyyy", 2, InputDate)
oFF("FinalDate").Result = DateAdd("d", -1, IDate)
End Sub

Note.  You will probably want to include code that will alert the user if an
invalid date is entered or to ensure the fields are not left blank.  Either
will throw and error in the simplified code above.