Select Write from the Block menu to saves the selected portion of the file you are editing into another file. If the other file already exists, EditPad will show a warning and if you confirm, the other file will be overwritten with the selected portion of the current file. If you want to add the selection to the file rather than overwrite it, use Block|Append instead.
If you do not specify an extension for the filename, EditPad will add one depending on the selection you made in the filters (the bottommost drop-down list) in the Block|Write dialog box. If the active filter is "any file" (*.*), no extension will be added. If any other filter is active, the default extension for that file type will be added to the filename. The default extension is the first extension listed in the Extensions setting of the file type's settings.