Some of the most common PDF tools leave a digital mark when the text has been edited after the initial export. When we find such a digital mark on a document, you'll see the 'Edited text' result. Clicking on the result will allow you to view each of the affected pages, together with regions we believe are most likely to have been edited. 

When the 'Edited text' signal is shown, we are certain that some text has been edited. However, the regions we highlight are only our best guess at what has been changed. It's possible that not all regions that have been edited will be highlighted, and that not all highlighted regions will have been edited.

Sample visual output is shown below.