I'm using Word 2016 and I'm trying to add a ribbon of custom buttons for a specific document.
I'd like the new ribbon to show up below the standard ribbon if I can.
If I have to add them below the existing stuff in the Home tab that'd be fine.

I've looked here and on google & so far I have no idea how to do it.

Can I add a ribbon of custom buttons in a specific doc in MS Word 2013+ ?
If so, how?

Adding QAT buttons to a specific document or template is much easier than is doing so on a Ribbon Tab.
Modifying the QAT in Microsoft Word

Adding a custom ribbon tab to a document or template is certainly something that can be done, but not through the Word interface. It will require XML modification together with vba work.
Customize the Ribbon (It doesn't take rocket science)

For more, see RibbonX: Customizing the Office 2007 Ribbon by Robert Martin, Ken Puls, and Teresa Hennig
This says 2007 but virtually all of it applies to Word 2016.

Thanks. This seems to have worked.
The QAT should be fine for my client's purposes.

Glad to have been of help.