If whilst editing a document you make a mistake or change your mind, you can use Undo to correct your errors. Use Redo to correct any Undo errors.
Choose Edit > Undo to backtrack your most recent editing step, or use Undo repeatedly to go back as many editing steps as you like.
Choose Edit > Redo to cancel your most recent Undo and reinstate the corresponding edit that Undo had removed. You can use Redo repeatedly.
An alternative method of discarding recent edits is to close a file WITHOUT SAVING it. Do this by choosing File > Close Document. This will discard all of the unsaved edits that you have made since the last time you saved the document.