Roberto Panetta has revved Text Converter for the Mac to version 1.5. The $9.99 app converts various file formats (PDF, HTML, RTF, RTFD) to standard plain text using drag and drop.
Version 1.5 is optimized for macOS Mojave. It also includes bug fixes. Text Converter require macOS 10.10 or higher and is available from the product website (http://www.ecleti.com/osx/totextconverter/) and the Mac App Store.