Word document does not offer Open / Save but shows as garbage in IE11 (or Edge) window

I am working with a website which makes document files available to download/view.
A button redirects to a URL - http://<server>/<folder>/<file>.doc

In Firefox this results in a dialog offering me the option to open the file in Word or to save it locally, which is ideal behaviour.

In IE11 (on Windows 7 or 8) and Edge (on Windows 10) the file content is displayed as text.

However, If I type a local filename into the address bar I get the Open / Save / Save as dialog that I would also expect in this circumstance,

How can I (or the website developer) persuade IE11 and Edge to give this dialog for a file coming from the website.

Note: The issue applies equally to .doc, .docx and .ppt files.

Thanks for any help.

Bill Manville. Excel MVP, Oxford, England. www.manville.org.uk