This feature is hard-wired into Word. So, though you can’t directly stop it, i.e. through the menu options, we have some macros that work around it.
Macro to Update all Fields in a Document
The code is as follows:
Dim oStory As Range
Dim oField As Field
On Error Resume Next
For Each oStory In ActiveDocument.StoryRanges
For Each oField In oStory.Fields
On Error GoTo 0
Select Tools, Macro, Create New Macro.
Name the macro.