Is there a way in Emacs (version 24.2.1) to bind a function key to the CTRL key? For example, I want to be able to type something like < F11 >-x < F11 >-f to open a file.
Making a non-control key into a control key is not possible from within Emacs. I think this must be done at the OS level.
On Ubuntu, you should be able to do this through xkeycaps, available from the repositories. Run the program, left click on the control key, select 'duplicate key', then select the F11 key. The F11 key will now respond as another control key. Note that this will be in effect for all programs, not just Emacs.