How to intercept data from a SharePoint form?

Question

JavaScript

There is a project on SharePoint. On the standard form, we attach the file with the file uploader. You must process the attached file before submitting the form. The third party script cannot access the file. How to be? The author of the form also cannot figure out how to pass a link to the file.
Alternatively, we want to write a third-party form that will process the file and other data. Problem: How to pass data processed by a third-party form back to the form or to the SharePoint database.

Answer 1

Ummmm, your form is not standard, but InfoPath (This is complete trash!). What is meant by process file?