If you want to fill display and value with different values then you will need to adapt Graham's code. I would use something like this:
Sub FillCC()
Dim oCC As ContentControl
Dim xlApp As Object
Dim xlBook As Object
Dim LastRow As Long, i As Long
Const strWorkbookname As String = "D:\DDL Entries.xlsx"
On Error Resume Next
Set oCC = ActiveDocument.SelectContentControlsByTitle("ddlServiceCat_1").Item(1)
If oCC Is Nothing Then
MsgBox "The CC you want to fill does not exist."
GoTo lbl_Exit
End If
Set xlApp = GetObject(, "Excel.Application")
If Err Then
Set xlApp = CreateObject("Excel.Application")
End If
On Error GoTo Err_Handler
Set xlBook = xlApp.Workbooks.Open(FileName:=strWorkbookname)
xlApp.Visible = False
LastRow = xlBook.sheets(1).Range("A" & xlBook.sheets(1).Rows.Count).End(-4162).Row
With oCC
.DropdownListEntries.Clear
For i = 1 To LastRow
.DropdownListEntries.Add xlBook.sheets(1).Range("A" & i), xlBook.sheets(1).Range("B" & i)
Record_Skip:
Next i
End With
xlBook.Close wdDoNotSaveChanges
lbl_Exit:
Set xlBook = Nothing
Set xlApp = Nothing
Set oCC = Nothing
Exit Sub
Err_Handler:
Debug.Print Err.Number
Select Case Err.Number
Case 6214 'Repeat entry.
Resume Record_Skip
'Or
'Msgbox "Repeat entry. Terminating process"
'oCC.DropdownListEntries.Clear
'xlBook.Close wdDoNotSaveChanges
'Resume lbl_Exit
Case 1004
MsgBox "The Excel file does not exist."
Resume lbl_Exit
End Select
End Sub