Digital signatures provide a means to verify that the documents have not been changed since the signature was applied. They use cryptographic algorithms to create a unique signature for the content of the document, which can be verified using the signer's public key. If the document content changes after the signature is applied, verification will fail, indicating a potential integrity violation. Hashing algorithms alone cannot tie the integrity check to an identity and do not provide non-repudiation. Encrypting document content protects confidentiality but does not by itself provide a way to verify integrity or detect alterations. File system permissions control access but do not provide a mechanism for ensuring or detecting whether file content remains unmodified.