Aliases which will you created in the table, we can't able to reuse in the same table.
Try this below code using original field name in where condition.
No_ as [Item],
"Sell-to Customer No_" as [Sell-to-Customer],
"Document No_" as [Invoice Number]
FROM ["our database".qvd]
WHERE "Document No_" <> 'Credit-1234' ;