If you want to compare one document with an earlier version, and you have both, do the following.
Open the first document in LibreOffice Writer.
When it is open, go to the menu above the document.
Click Edit
On the pull-down menu, click Compare Document ...
A file open dialog will appear.
Use it to open the earlier document. Writer now has a document that shows the changes from one to the other.
Scroll through the result and see how the changes to the older document that result in the newer one.
You can save this as a third document if you want. Or you can always make another comparison again.
This may not be exactly what you are looking for, but it is very useful to know about.
- Dennis
Also, in working with a document, you can record changes as you do it. You can see the changes (show them as you type), or you can simply record them. Then you can show them whenever you want, change your mind, etc. This is on the Edit | Changes dialog. Turn on Edit | Changes | Record and the changes you make from then on are remembered and can be shown.