Hello,
What version and license of phpdocx are you using? Your username doesn't have any license tied, please send to contact[at]phpdocx.com the username or email of the user that purchased the license you are using.
Also please note that the DocxUtilities class is only available in Advanced and Premium licenses. Using the searchAndHighlight method with an array was added in phpdocx 12.5 (https://www.phpdocx.com/news/post/phpdocx-v12-5-release-notes/224):
DocxUtilities: searchAndReplace, searchAndRemove and searchAndHighlight methods allow using arrays (Advanced and Premium licenses).
Regards.