Hello,
That method uses altChunk tags, that are only supported by MS Word 2007 or newer on Windows. This way of adding external files is handled by MS Word, although you can set matchSource as true (https://www.phpdocx.com/api-documentation/templates/replace-variable-external-file-Word-document) some styles won't keep.
If you are adding HTML, we recommend you to use native methods that transform HTML to Word:
https://www.phpdocx.com/api-documentation/word-content/embed-html-Word-document-with-PHP
https://www.phpdocx.com/api-documentation/templates/replace-variable-html-Word-document
If you need to add DOCX documents, you can use the mergeDocx method to keep content and styles:
https://www.phpdocx.com/api-documentation/docxutilities/merge-Word-documents-with-PHP
Regards.