Although Windows itself will allow you to assoicate any extension or number of extensions with any applications this can soon become limited in its scope. I have found it useful to be able to choose which application to open a file with not only on the basis of a defined extension, but on a pattern of extensions, or on its file name or path. It was in order to achieve this functionality that SmartOpen was created.SmartOpen can associate itself with any existing extension, including the special types "All unknown files" and "All files", or create new ones all from an easy to use interface. Each extension can have multiple conditions which can contian the wildcards * and ?, and will operate on the full file name, extension and path. Each condition can execute multiple actions sequentially, or display a pop up menu to offer a choice of actions.SmartOpen can be used for a huge variety of tasks, but for three suggestions take a look at the online tutorials provided. Better yet, download it and experiment to find settings useful to your way of working.