1. A method executing in a pen-based computing system, the method comprising: scanning a printed document using a scanning device; identifying a background pattern in the printed document based on a result of the scanning; based on the background pattern, determining identification of an electronic document corresponding to the printed document; determining, using a processor, based on the identification of the electronic document, an electronic version of the electronic document; and triggering an alert, if the determined electronic version of the electronic document is an invalid electronic version of the electronic document.