How to compare two text files?

Question

Text Processing Automation

There are two texts, they are almost the same. For example, a long article. This is the first file.
Then this article was copied 100% without editing, and plus new information was added (at the end, in the middle - everything from a new line, new paragraphs).
So, the task is to find out:
1. What text was added.
2. Was a part of the main text lost during editing?
Roughly speaking, the first file is like this:

Ask the right question in the Toaster.

.
Second file:

Ask a question in the Toaster. But word it in such a way that it won't be removed .

As you can see, in the first text they added "But formulate it so that it is not deleted."
At the same time, the word "correct" was removed from the first text.
The question is how to automatically find out if the text is very large and there is not enough time to manually check it?

Answer 1

Any utility that googles for the diff keyword in its name.
Or online services.
Both highlight changes.