Krdc is one of a pair of KDE programs - Krfb is the other. Krdc lets you log onto another computer remotely; either over a LAN or over the internet. Krfb lets you share your desktop through the local network with another user, probably somebody like the tech downstairs who you want to help you. Sharing your desktop can let her help you figure out something you are having trouble with. You can call the tech on the phone and be talking with her while she assists you. The tech can even "drive" your computer if you decide to let that happen.