mrmacfixit,,
I am afraid I must admit my ignorance and apologise for any of your valuable time I may have thereby wasted. My inability to open "Preview" was,I now find, entirely due to my not understanding how it "worked". I had been clicking on the icon and nothing was happening. I have now discovered, after two days of frustration, that any PICTURE (and for all I know yet, OTHER THINGS OF SIMILAR NATURE), that I open, ARE OPENED(by default) by "Preview". I can then do all the things mentioned in the Apple article!
I hope no-one at CNet will hold this against me when, in future, as I know I shall, I need help with something. Many thanks.