Hi,
To hide certain buttons in the viewer, please refer to this guide https://pdfjs.express/documentation/ui-customization/hiding-elements.
In particular, highlight buttons have data-elements such as highlightToolButton, highlightToolButton2, etc and you can pass them to the instance.disableElements API call.
In the latest version we’ve added data-elements to the color palette and the opacity slider, so you can use disableElements to hide them based on the current tool as well.
Best Regards,
Zhijie Zhang