Have a Promissory Contract of Purchase and Sale/Contrato de Promessa de compra e venda drawn up, to be signed by you and the vendor. It should include:

• Identification of the parties.
• Identification of the property.
• Agreed terms and conditions of the contact

You will normally have to pay the vendor a minimum deposit of 10% of the full purchase price at this stage. The contract is signed in front of a Notary/Notário. It is legally binding on both buyer and seller. If the buyer defaults he forfeits the deposit. If the seller defaults he has to pay the buyer double the deposit. Or, if a clause of Specific Execution is included, the vendor cannot withdraw and the purchaser can legally force the vendor to sell to him).