Assuming that the customer number is in the body of the selected message, and is exactly in the format described i.e. all numeric, the following will locate it and copy it to the clipboard:
Option Explicit
Sub GetCustomer()
Dim olItem As Outlook.MailItem
Dim olInsp As Outlook.Inspector
Dim dCust As DataObject
Dim wdDoc As Object
Dim oRng As Object
Dim sCustomer As String
Dim bFound As Boolean
On Error GoTo lbl_Exit
Set olItem = ActiveExplorer.Selection.Item(1)
With olItem
Set olInsp = .GetInspector
Set wdDoc = olInsp.WordEditor
Set oRng = wdDoc.Range
With oRng.Find
Do While .Execute(findText:="Customer #:[ 0-9]{2,}", MatchWildcards:=True)
sCustomer = Trim(Split(oRng.Text, Chr(58))(1))
bFound = True
Set dCust = New DataObject
dCust.SetText sCustomer
dCust.PutInClipboard
MsgBox "Customer number '" & sCustomer & "' copied to clipboard"
Exit Do
Loop
End With
If Not bFound Then MsgBox "Customer number not found"
End With
lbl_Exit:
Set olItem = Nothing
Set olInsp = Nothing
Set wdDoc = Nothing
Set oRng = Nothing
Set dCust = Nothing
Exit Sub
End Sub