The following procedure does not work with Word but the end result is compatible with Word so the redacted document can be opened in Word afterwards: -

Use LibreOffice Writer to redact Word documents. See How to use document redaction in LibreOffice 6.3.0.4 - TechRepublic

Note that LibreOffice is now on version 7.2. See Home | LibreOffice - Free Office Suite - Based on OpenOffice - Compatible with Microsoft

It is proper redaction and may be an acceptable workaround?