Digital Signature is a technology used to detect forgery and tampering of digital documents and to verify the creator.
If the hash value of the original document (data) created by the sender and the hash value of the document (data) actually received by the receiver are the same, the receiver is proved to have received the real thing.
This process allows us to confirm that no tampering has occurred to the data.
In Bitcoin, this is used to prove ownership of the coin and to transmit transactions. The signature of the bitcoin owner is recorded on the blockchain, and the owner can only be rewritten if the signature matches.
Even if a fraudulent attempt is made to record an insubstantial transaction on the blockchain using a false signature when the owner does not have the bitcoins, the transaction cannot be rewritten unless the signatures match.
A signature is not an actual signature with a pen, but an electronic signature on data.
When the signature is made, the public key to verify it is also written, and by checking the signature and the text, it is possible to confirm that the signature has not been tampered with.