Sentences not recognised

Studio 2017 SR1 Build 14.1.6413.8, Windows 10.

I am working on a Word file that has been converted from a pdf.

Repeat sentences are not being recognised. When I use the concordance I get the above - there appear to be hidden tags.

What are they, and is it possible to eliminate them? I very frequently work on converted files, but this is a new experience.