There is a dearth of browser inline editors for Word documents.  It appears that the only viable solution currently out there is to implement WOPI and this standard is complex, poorly documented and extremely difficult to implement.  There are some alternatives out there:

• https://www.zoho.com/officeplatform/integrator/wopi-alternative.html
• https://www.collaboraoffice.com/code/

The former is incredibly expensive because it charges per API call (effectively charging each time a document is opened or edited) and the latter is overly complex and for Linux users.

A further alternative is syncfusion's document editor.  This editor is good but loses formatting.

Surely it would be possible to unravel Word's open xml format and load it into a modified version of the Rich text Editor?