Performing a factory reset is a bit more implicated on an iMac now because of a hardware omission setting in it. The device is no longer equipped with a built-in optical disc drive. Even if you have the OS reinstallation DVD, it won't do you anything unless you have an external optical drive connected to your system. Restarting or rebooting iMac to its Factory Settings cleans the entire contents of its memory, including stuff you copied to the clipboard. For this, you can also take technical support assistance from Apple iMac factory reset page that helps you reboot iMac to its defaults settings in a competent manner.
https://sites.google.com/a/allitemarketing.biz/apple-online-support/800-961-1963-get-help-and-support-to-restore-reboot-macbook-or-imac-to-factory-default-settings
