I'm not sure that formfield dropdowns will work in this case, as they only accept a maximum of 25 entries and there are more than twice that US States.
As for the tax calculation, with formfields no VBA code is required - it can all be done with field coding. Such a field might be coded along the lines of:
{={IF{REF ddCountr}= "CA" {IF{REF ddRegion}= "ON" 1.13 1.05} 0}*{Half_Fees} \# $,0.00}
Regardless, given the limitation of 25 for formfield dropdown entries, you should instead consider the use of content control dropdowns, for which all your US States can be added. In that case, the VBA code might look like:
Code:
Dim Admin As Single, Tax As Single
With ActiveDocument
If .SelectContentControlsByTitle("Country")(1) = "US" Then
Tax = 0
Else
If .SelectContentControlsByTitle("Region")(1) = "ON" Then
Tax = 1.13
Else
Tax = 1.05
End If
End If
Admin = .SelectContentControlsByTitle("Admin")(1).Range.Text
With .SelectContentControlsByTitle("Tax")(1)
.LockContents = False
.Range.Text = Format(Tax * Admin, "#,##0.00")
.LockContents = True
End With
End With
Note: You shouldn't use content controls and formfields in the same document, as they weren't designed to be used that way and trying to do so can cause problems.