Thanks for the due diligence.  I can see how this could be used as a solution but it's effectively a bit of a bodge.  The user loses the essential ability for pagination and editable/non-editable areas (amongst a whole host of other features).  In a document management solution, these are fairly essential.  The key for me is to allow users to edit documents that they are familiar with.  I worked with WOPI for two months before throwing the entire work effort out the window.

I enjoy working with Kendo products and have been doing so for over ten years although I have never liked your approach to responsive design - I think this is a hangover from selecting a different container model to Bootstrap (I seem to remember this from a long time ago).  To this end, I was hoping that your Angular component set might be written from the bottom up with a different design approach but it appears not. Anyway, I diverge.

Bringing the Docx document into the editor would be a great option if it displayed it as a page with editable regions and pagination.  As far as I can see Syncfusion is well behind Progress in terms of the overall offering and support but in this one component they are well ahead.  Their approach is to mirror the OpenXML format of Word with their own .sfdt format and deliver that to be edited inside a component which is obviously a variation of their own editor.  That's the way forward for Progress, along with a big marketing message to the developer community saying "Your WOPI woes are over....".  I personally deliver these documents from blob storage and mirror the results on my customers' local file server with a simple Powershell command, that way they have a local copy of all the document collection as a backup for disaster recovery.

It's a learning curve with Syncfusion, one which I didn't want to have to undertake.  But that's the way I have to go whilst Progress has no document editor.  Strange really when you are so close with your editor and WordsProcessor library and offer a spreadsheet in almost every flavor.  WOPI's a real pain and impossible to implement and a document editor would really shake things up...

In my humble opinion.