Thanks to you who responded — and so quickly too. Have tried a trial sample of 10 books which I sent specifically to my K3 from Manage Your Kindle. I then connected my K3 to my computer and added the books via calibre (with K3 selected as my device in Welcome Wizard). Worked like a charm!! It would appear that now all I have to do is perform the same operation with my remaining 440 books!! It will be a laborious task but, thankfully, not a mentally taxing one. Luckily tomorrow is a holiday (Cdn Thanksgiving) so shall just concentrate for an hour or so and it will be done.
Thanks again for your help.