Variables aren't on documents. You have add a DocVariable field to the document e.g., {DocVariable SomeDocumentName} then call an auto procedure then the document is opened or a new document is created from the template:
Code:
Sub Document_New()
ActiveDocument.Variables("SomeVariableName").Value = InputBox("Enter the variable value")
ActiveDocument.Fields.Update
End Sub
Sub Document_Open()
ActiveDocument.Variables("SomeVariableName").Value = InputBox("Enter the variable value")
ActiveDocument.Fields.Update
End Sub
You could also use a bookmark, content controls, formfields or a userform:
http://gregmaxey.com/word_tip_pages/..._userForm.html