How can I send files/folders to people who do not have a Koofr account?

You can share files/folders with people who do not have a Koofr account by sending them a link. See how to do that in How can I share a file? or How can I share a folder? under option Send link. They will be able to download the file/folder without registering.

Note: If you share a file/folder through Add People, they will have to register to Koofr, to be able to view it.