It's an option that either is available to you at Checkout or not. Here's some details from the User Agreement:
The Pay After Delivery payment option allows qualifying buyers to purchase eligible items and wait up to 14 days to pay for them. The PAD payment option is only available for eligible purchases under $10,000.00 and is not available to all buyers. In order to use PAD, qualifying buyers must have a valid checking or other qualifying account at a bank which is linked to their PayPal Account and identified as their primary bank account from which funding transfers may be withdrawn; if there is no valid linked bank account then PAD will not be available, even if the qualifying buyer has used PAD before. Where a buyer and item purchased are eligible for PAD, which shall be determined in PayPal's sole discretion, buyer may choose the PAD payment option at the time of purchase. Although PayPal will not impose a fee for a buyer's use of PAD, it is possible a third party, such as the financial institution holding the primary bank account, may impose a fee in connection with the payment or purchase, in addition to the amount of the transaction.
