Thank you for your answers.
I'm not sure what you mean by 'open the PDF with K4PC' or 'open the file with K4PC.' Perhaps you could explain this in more depth?
I did indeed copy the PDF into the K4PC folder and it did work. The book then showed in the Kindle. When I opened the book in the Kindle, the writing was tiny and hard to read. Can this be changed? Can you add a cover for the book in the Kindle as you can in Calibre?
Have you got the link to 'Alf's blog for more about DRM and Calibre?'
What I would dearly love to do is, somehow transfer the books from the K4PC to Calibre. I find it much easier to read books in Calibre once I get them in there. Can this be done and can you give me a detailed explanation on how to do it please?
How do I export books from the K4PC to Calibre? I do not understand when you say, 'Use MOBI as the output format for the Kindle.' I am new at all this so could you explain this as well please and what I should do as your explanation?
Just to let you know, I have Calibre (to manage my books) and Nook as well as K4PC.