The first issue to address is that the selected reference in document to be edited does not appear in the table, so it is never going to work. The problem is that there are assorted non-breaking spaces in both documents that interfere with the string matching. The suggested code addresses that issue and makes changes to both documents before string matching.
Put the path of 'Dokument2.docx' in the line
Set oSource = Documents.Open(Filename:="C:\Path\Dokument2.docx", _
AddToRecentFiles:=False, Visible:=False)
It doesn't matter whether that document is open or not when running the macro. Select the reference to be updated and run the macro. If the reference is found it will be updated according to the criteria you posted. If not found, you will see a warning message. Dokument2 is then closed without saving the changes incurred by the macro. The macro doesn't save or close 'Dokument1'
Sub Macro1()
'Macro by G Mayor 23 May 2015
Dim oDoc As Document
Dim oSource As Document
Dim oRng As Range
Dim oFind As Range
Dim strReference As String
Dim bFound As Boolean
Set oDoc = ActiveDocument
Set oRng = Selection.Range
oRng.Text = Replace(oRng.Text, Chr(160), Chr(32))
strReference = oRng.Text
If Len(oRng) < 6 Then
MsgBox "Select the reference first!", vbCritical
GoTo lbl_Exit
End If
Set oSource = Documents.Open(Filename:="C:\Path\Dokument2.docx", _
AddToRecentFiles:=False, Visible:=False)
Set oFind = oSource.Tables(1).Range
oFind.Text = Replace(oFind.Text, Chr(160), Chr(32))
With oFind.Find
Do While .Execute(FindText:=strReference)
bFound = True
oFind.MoveEndUntil "("
oFind.End = oFind.End - 1
oRng.Text = oFind.Text
Exit Do
Loop
End With
If Not bFound Then
MsgBox "The selected reference was not found in the reference table.", vbInformation
End If
oSource.Close 0
lbl_Exit:
Set oDoc = Nothing
Set oSource = Nothing
Set oRng = Nothing
Set oFind = Nothing
Exit Sub
End Sub