The form “Tor Tor 3” is an official bank document, which you can get from the bank only after changing a foreign currency; or in case you have a Thai bank account and you sending the funds from your country to Thailand, after you arrive to the Land of Smiles you can request this form (Tor Tor 3) from the bank branch where you open an account before. The amount stated in this document shows how much money you send from your country, or amount of currency you changed into THB in the bank.
The “Tor Tor 3” is required only for buying a property, so when you request it from the bank, this form must have a remark: “for the purpose of purchasing a property”. This document has to be provided in Land Office on the day of transfer the ownership rights.