Supposedly a web application mostly uses javascript in order to execute programs in your local environment. Those programs work with your files - whatever type the file shall be.
I'm brought to think that it doesn't store your files in some server and that it opens them in a temporary folder on your pc (like AppData or similar), according to some examples.
Does the reading, modification and output of the new file occur inside your local environment or is the information transferred to a remote server in some step of the process, maybe like some sort of backup?
My question also concerns a possible register of modifications applied to the file. Usually there's always a history of actions the program does in order to process the file and I wonder if the website would transfer it to their servers - statistical analysis for example - instead of keeping it local aswell.