It is possible to view an eCTD with a web browser with Adobe Acrobat reader installed. However, this is not ideal, as each eCTD backbone can only be viewed in isolation. Critically, it does not provide any automatic indication of whether a document being viewed in a particular sequence has been replaced or deleted in a later sequence. Review tools are available that use the information in the XML backbones in each sequence to display a "composite" view of all sequences showing only documents that have not been replaced or deleted. A free basic viewer is available from Gecco.