Is share buyback compulsory?

No, share buybacks are voluntary events.

Under share buyback, a company offers to buy back a certain number of shares. However, the shareholder can choose whether to sell all their shares, sell a part of their shares or ignore the offer. The shareholders don't need to participate in the offer.

In the cases where the buyback price is significantly higher than the market price, the buyback issue oversubscribed significantly. In the case of over-subscription, buyback is done on a propionate basis by investor category (Retail or HNI). For example, the TCS buyback acceptance ratio is hardly 25% in retail and 2.5% in HNI most of the time.