by Davo Smith.
Do you meant to deleted the folder /mod/assign/feedback/editpdf from the code on your server?
If that is what you've done, all you need to do is download a fresh copy of Moodle from: https://download.moodle.org/releases/latest/ (if you are not using Moodle 3.9 at the moment, then use one of the links on the right-hand side of the page to find the version you are on).
Once you've downloaded the code, unzip it, find the /mod/assign/feedback/editpdf folder in the downloaded code and upload it to your Moodle server.