A contract concluded in the form of a contract in accordance with Article 32 of the Contract Law of People's Republic of China (PRC) shall be established when both parties sign or seal it. Article 44. A legally established contract shall have legal effect upon its establishment. Where approval and registration procedures are required by laws and administrative regulations, such provisions shall prevail. To sum up, a citizen's personal seal is only valid if the citizen himself uses his own seal to carry out a civil legal act. And when the citizen seals the relevant legal documents, there are no invalid or revocable or changeable civil legal acts such as fraud, coercion, major misunderstanding and obviously unfair. The act of stamping is the expression of the true meaning of citizens. In this case, the act of stamping was established according to law. A legally established civil juristic act is legally binding on citizens. Answer to the supplementary question: the judicial principle is that the principle of contract formation is to sign or seal, either of which can be done, but not both. As long as the process of stamping by the other party is truly expressed, there is no problem.