Hi Thibault,
Thank you for contacting Syncfusion support.
Currently our Essential DocIO doesn’t have support to work with Word documents in JavaScript or PHP. We have already logged this requirement as feature request. We will implement this feature in any of our upcoming releases. We usually have an interval of at least three months between releases. The feature implementation would also greatly depend on the factors such as product design, code compatibility and complexity. We request you to visit our website periodically for feature related updates.
As a workaround, you can implement web service using Essential DocIO with web API approach to process with Word documents. Kindly refer our online sample for Mail merge with form request using Web API in the below link, and let us know if this helps you.