Word 2013 - comparing documents does not show changes in new document

[MFL100]

When I use Compare in the Review tab to compare two documents, the differences between them do not appear in the text. No redlining shows. The only indication of changes are lines in the border of the document. Because I have used Compare for years in different versions of Word and it is so easy to use, I suspect that my software is defective.

Any suggestions?

Thanks.