Is this really the name of the property:
"RandomNumbe r"
The following creates a new document based on the template and places a new random number in both the template and the new document just created.
Code:
Sub AutoNew()
Dim lngNewRandNumber
Randomize
lngNewRandNumber = Int((1000 * Rnd) + 1)
'Updates the template property.
ThisDocument.CustomDocumentProperties("RandomNumber").Value = lngNewRandNumber
'Updates the document you have just created.
ActiveDocument.CustomDocumentProperties("RandomNumber").Value = lngNewRandNumber
End Sub