Stamp duty is charged on documents connected with conveyance on sale, agreement for sale or lease of immovable property, and share transfer. 

For the first three situations, all parties and all other persons executing such transactions are liable for stamp duty. For share transfer, the agent or the principal affecting the sale or purchase of stock is liable for stamp duty of the contract note for that transaction, while the transferor and transferee are liable for stamp duty of documents connected with any other kind of transfers. 

The stamp duty rates depend on the type of transaction. 

References:

1. Stamp duty rates: https://www.gov.hk/en/residents/taxes/stamp/stamp_duty_rates.htm