We have purchased multiple downloads of this software in the past online at Adobe.com but now I can't find it anywhere. When I reach out to the link on the page for more information, I get directed to a 3rd party retailer that wants me to pay an additional fee to get the Adobe product. This is poor business procedures on Adobes part. Id you are going to make your products more difficult to get, I'll more than likely be looking for an alternative product.
The fact is, that Designer ES4 is already 5 years old and Adobe has stopped to sale it a few months ago. The latest version of the Deigner is available under its new name AEM Forms Designer 6.x. However Adobe doesn't sell it stand alone anymore only together with Adobe Experience Manager (AEM), I'm afraid.