In contrast to the Audio editor, the Wave editor makes permanent changes to your audio files, (sometimes called “destructive editing”). When you for example Paste in the Wave editor, this alters the file on disk directly, rather than just adding new segments or Events.
You can of course Undo the last action in the Wave editor. However, you might want to experiment with different editing operations in the Wave editor, and later decide to go back to the original file. If you do, use the Duplicate File item on the File popup menu in the Pool to duplicate your audio files before editing them in the Wave editor.