File types in Windows will often have an open & print action associated with them. Not all will have 'edit' action- this can be added or changed using the operating system's option below: Folder Options [File Types]>Select extenstion>Advanced
Now the Edit File Type dialog will appear. Select New and add an action called "edit" and browse for program to be launched. These actions will appear in the context menu of windows explorer. Default actions can be changed here also (which should be shown in a bold font).
Example:
My .bmp files have only an "open" action associated with them. I added Firefox as the "edit" action to test if Xnview will now start that program using F4. It did.
