if you want CTRL+F to be a shortcut for Find ( I do ) ( 2014 )
Tools > Customise > Interface
Expand Keyboard Shortcuts
You will see two sets, Shortcut Keys and Temporary Override Keys
If you expand all the Shortcut Keys, you will see all the CTRL shortcuts
If you expand the Temporary Overrides, you will see no CTRL shortcuts.
That's because you can't actually make CTRL short cuts in the Temporary Overrides page. Acad won't let you. Try, Create a Temporary Override, navigate to the Properties Box, Highlight Keys, click on the box on the far right to open a dialogue, you can't press CTRL+F, you can make a SHIFT shortcut.
BUT
You can overwrite an existing Shortcut key. There seem to be a couple that I never use eg CTRL+H.
Rename CTRL+H ( or another one ) to 'Find', go to the Properties box below, highlight Keys, open the Keys dialogue Box ( icon on the far right .. three dots ) and press CTRL+F, then Okay...
You're done : you now have CTRL+F as a Text Find shortcut