What is .PDE file extension?
Software application written with Arduino, an IDE used for prototyping electronics; contains source code written in the Arduino programming language; enables developers to control the electronics on an Arduino circuit board.
To avoid file association conflicts with the Processing software, Arduino changed the Sketch file extension to .INO with the version 1.0 release. Therefore, while Arduino can still open ".pde" files, the ".ino" file extension should be used instead.
You can see a list of software programs here on www.easyfileopener.org that can open this file type so that you don’t need to search for it on the web. You can then open your file with this extension using a software listed below.