Can I send a copy of an i-book to a friends Mac or PC?

The information on iBooks, http://support.apple.com/kb/HT5557 does not say anything about sharing iBooks. That certainly isn't possible with a PC since the books would not be able to be read.

The only possible way looks like giving the person access to your iCloud account so they can download the books from there. That would not be a very good security thing to do, however.

I think only sharing currently allowed is covered by this

http://www.mcelhearn.com/os-x-10-9-mavericks-sharing-your-ibooks-library/

If your ibooks have no DRM and are in the .epub format, then you can of course just send the file to anyone you want. But paid-for books are almost never in that category.

As another senior citizen, you are most welcome.