Text Highlight behaves as Text Redaction Annotation for Word documents but works fine for PDF files.
To test the annotation I used the AddTextHighlightAnnotation test class. I just had to change input and output files, changing it to a doc file (lines 21, 23). It seems that the backgroundColor and opacity properties (lines 49, 53) are being ignored for Word documents.
Git project: https://github.com/groupdocs-annotation/GroupDocs.Annotation-for-Java.git
Git branch: master
Git revision: 72a3efe9
SO: Windows 10
Java version: 1.8.0_281