I cannot find the Microsoft Office Desktop Apps program by your route. To answer your other questions…
PDF files right-click fine
Doc files right-click fine
Old Excel files right-click fine
I suppose the answer is to uninstall Office 2003 from my Windows 10 laptop and stick to LibreOffice.
I rarely use the new laptop actually, an HP Elite 360 which in many ways I really dislike I prefer my 8-year old Samsung RF511, much more comfortable. But I may be travelling soon and the HP is of course much lighter, and I will need something with me that can open these modern Windows file formats.