"could this be applied to disable user entry into all fields in specific
sections? "

Yes, by doing it by Section.  Say you have formfields in Section 1 and
Section 2.  The document is protected for forms, with ALL formfields are
active (and enabled).

Say the user puts in information into the formfields in both Section 1 and
Section 2.

Sub SpecificSection()
Dim oFF As FormField

For Each oFF In ActiveDocument.Sections(1).Range _
             .FormFields
  oFF.Enabled = False
Next

For Each oFF In ActiveDocument.Sections(2).Range _
            .FormFields
  oFF.Enabled = True
Next
End Sub

Would now permit users to alter/change the formfields in Section 2 (enabled =
True) but not Section 1 (enabled = False).

The questions is, though, where/when would you execute the above code?  You
could do it as the OnExit macro for the last formfield in Section 2.  That is,
the user puts something into the last formfield in Section 2, and boom...
Section 2 is enabled but Section is disabled.

The problem with that is the user could easily do the last formfield in
Section 2 before anything else...before putting something into Section 1.

You could add testing that checks first (have Section 1 formfields been
filled?), but that would greatly add to the logic.