This is a problem common to all types of documents, not only to Print2Flash documents. You can prevent caching in the browser by sending these HTTP headers when returning Print2Flash documents from your web server:
Expires: Mon, 26 Jul 1997 05:00:00 GMT
This will make common browsers such as Internet Explorer or Firefox not to cache the documents. However, there are offline browsers that always cache downloaded files regardless of the headers. An example of such a browser is Ad Annihilator (http://adannihilator.com). To circumvent offline browsers caching, it is needed to implement a custom solution at which Print2Flash would ask permission from the web server to display the document at each loading. This requires custom development and knowledge of your site details. Contact us if you are interested in this kind of solution.