Can PureRef be on top of all windows? if yes, then explain how to do it. If not, then this function should be.

For sure, you can find the option in the right click menu under Mode->Always On Top or with the keyboard shortcut Ctrl+Shift+A.

Check out the keybinder in the settings dialog for more shortcuts and the option to change them to whatever you woul like. The about page on this web page also lists all available shortcuts for a better overview.