use https://[host]/p/[padName]/export/txt to get the text ,save to local storage/file_system
from this
https://github.com/ether/etherpad-lite/wiki/Backing-up-and-Restoring-Etherpad-Lite-Pads
Thanks!
maybe it's possible to change the div to textarea in padview.html , <textarea id="pad" class="active">