To edit file selected in panel go to File(s) > Edit. The command by default opens the file in an internal editor. You can make the command open the file in any external editor in preferences. From submenu File(s) > Edit (alternative) you can open the file in any of configured editors.

You can create new empty file using command File(s) > New > File. The command asks for name of the new file and then opens your default editor.

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