Contrary to a certain LOSER on here - To Cancel shares Share (Purchase agreement or SPA) the Company/CEO must arrange to have the shares acquired on the open market or privately - it is done to increase shareholder value, typically in two ways, either to redistribute it back as a dividend to shareholders or to cancel them all together.
The CEO/Company must first buy them off the open market or offer in private negotiations to buy them from Organizations / Groups (MMs) and even individuals