1)A signed the contract with digital signature and sent it to B;

2) Then, A's digital signature includes the original contract (in the form of hash value)+signature or seal appearance +A's private key (for easy understanding, the specific signature scenario is slightly different from the technical implementation).

In the third-party electronic contract platform, different signers use their own digital signatures to sign contracts with different original contracts (others' digital signatures may be added), so the digital signatures corresponding to each signing action are different.

Therefore, digital signatures cannot be reused.