Some expressions say "this agreement will come into effect after being sealed by both parties", so the seal is valid. Some expressions say that "this agreement will come into effect after being sealed and signed by both parties", so the signature is not necessarily the legal representative, but also the authorized representative of the company or the authorized agent of the legal representative. Secondly, it depends on the seal. If it is a special seal for the contract or the official seal of the company, it is generally valid if the contract does not stipulate that "this contract will take effect after being signed and sealed". In this case, there is no need to consider the identity of the signatory, because only the seal can be used. If there are provisions in the contract, it must be signed and sealed to be effective. It must be considered whether the signatory has the right to sign. If you have no right to sign, you can also consider whether there is an agency by estoppel. If so, the contract is also valid.