Word Template Automation Add-in

I need a custom add-in (macro, VSTO, or Office JS—whichever you favour) for Word 2019 or later that turns Word into a lightweight template engine.

Core workflow
• In Word I create a normal document containing standard paragraphs, tables, images, etc. Your add-in must let me mark variable fields inside that content.
• A separate XML model file describes every field/property. When I press “Load Model” the add-in reads the XML and shows the structure in its own window. From there I simply click a property to insert the appropriate placeholder into the document.
• The same window should also let me drop in control commands such as loops/foreach so I can repeat sections.

UI expectations
Two custom windows are required:
1. Model Browser – lists the loaded XML model, supports drag-or-click insertion of fields and commands.
2. Data Editor – opens a companion data file so I can tweak sample values inside Word before previewing.

Preview & external calls
A Preview button must:
1. Download the latest model and data XML from a given URL if I haven’t already.
2. Launch an external executable (I will supply the command-line syntax) to merge template + data.
3. Wait for the executable to finish, then automatically open the produced document in Word and PDF reader for inspection.

Nice-to-haves (optional, not mandatory)
• Window may float or dock; I have no preference, so choose what flows best with your framework.
• Progress or status messages during the download/build steps.

Deliverables
- Compiled add-in / macro ready to install.
- Well-commented source code and build instructions.
- Short user guide showing how to load a model, insert fields, add loops, edit data, and run Preview.

If you have prior experience with the Word object model, VSTO, VBA, Office JS, or similar document-generation tools, please mention it. Looking forward to making Word template creation much less manual!