Elsevier could easily make this completely non-trivial. For a very silly example, imagine how this would work if each user got a PDF using a different font. How do you automatically normalize the difference between Comic Sans and Times New Roman? Sure, it's trivial to write a tool that understands what "fonts" are and does this (especially for PDF), but you can't do it with a simple binary tool.
And of course Elsevier can do something entirely more complex.
Bad bad bad bad, again bad idea. That changes the structure and the meaning of the content. A single word replacement can change the context of the entire sentence which can change the content of the entire paper. Changing it can create unintended effects which can make Elsevier to thrash their reputation and universities will move on to different scientific/academic journals site.
If Elsevier tries this method with peer-reviewed papers, then it have to go through the reviews again to ensure that the original and the revision have the equivalent expression which is difficult to do. Authors chose those words and structure to convey their expression in those papers. They chose it for a reason and Elsevier is not going to risk their reputation to change the authors papers without affecting the content of the paper.