Suddenly, every time I try to open a PDF (or HTML) file, Word leaps in and coverts it to a Word document. I know can open it by right click and 'open with' but I normally open PDF file by double clicking on the name and the PDF file opens. Not a great issue but I'd like to go back the where it was.

Do you think it's possible you or someone else set the default program for those file extensions to Word? Go into Windows Explorer, find a PDF file, right mouse click and look at Open With. At the bottom it should ask you to choose the default program. You can make sure you open PDF's with Acrobat, or Acrobat Reader, and HTML files with your favorite browser.

I can do that but \I want to open it directly as before. Nobody else could possibly have reset anything to do with it and I couldn't unless it was by accident and I can't see that happening.

Doing as kilroyscarnival has suggested should allow future openings in your default PDF viewer/editor by d/clicking a PDF.
File associations can often get 'mixed up/changed' for one reason or another and often unknown reasons. It's should be very easy to sort out.
Give the suggestion a try.

Thanks. Works for PDF and seems to for HTML but why is retrieving HTML file so damned slow?

What do you mean by ". . . . why is retrieving HTML file so damned slow"?
Are you using a browser to open the HTML file?

I assume so as I always have Chrome open when I want to see any type.