Document integrity is the assurance that a document remains complete and unaltered from an identified state, such as the version approved, sent, or signed.
That identified state is important. A document may be edited legitimately while it is being drafted. Integrity does not mean a file can never change. It means changes can be prevented, controlled, recorded, or detected so that people can determine which version they are reviewing and whether it still matches the relevant reference version.
In a document-signing workflow, the reference state is often the exact document presented to the signer or the completed document produced after all parties have signed.
What document integrity establishes
Document integrity addresses two closely related questions:
- Is the document complete?
- Does it still match the identified version?
For a digital file, even a small change can create a different document state. Changes may include replacing a clause, deleting a page, adding a signature image, modifying a form field, changing metadata, or altering the file after signing.
A document with reliable integrity evidence may be described as tamper-evident. This means unauthorized or unexpected changes can be detected. It does not necessarily mean changes are impossible.
For paper documents, integrity often depends on physical custody, page numbering, initials, secure storage, and records showing who handled the original. A scan can preserve the visible appearance of a paper document, but it does not automatically prove that every page was captured, that the scan represents the original, or that the original remained unchanged.
How hashes detect changes
A cryptographic hash function processes a file and produces a fixed-length value, sometimes called a digest or digital fingerprint. The same file should produce the same hash when processed with the same algorithm. If the file changes, the resulting hash should also change.
A system can record the hash of the approved or signed version and compare it with a newly calculated hash later. Matching values provide strong technical evidence that the file’s bytes have not changed since the reference hash was created.
A hash alone has limits. It does not identify who created the document, who changed it, or whether its contents were accurate. The reference hash must also be stored securely. If an attacker can replace both the document and its recorded hash, the comparison loses much of its value.
Version control, access controls, and audit records
Document integrity usually depends on several controls working together.
Version control assigns revisions, dates, identifiers, or status labels to document states. It helps distinguish a draft from an approved copy and preserves the sequence of authorized changes. Version control supports integrity by making changes traceable, although it does not provide cryptographic proof by itself.
Access controls restrict who can view, edit, approve, sign, download, or delete a document. Permissions, account security, and authentication can reduce unauthorized changes. These controls are primarily preventive. They cannot, on their own, prove that a file remained unchanged.
Audit records document relevant events, such as creation, upload, viewing, editing, approval, signature, and completion. A protected electronic signature audit trail can connect a particular document version with the events surrounding its signing. An audit record is more useful when its entries are timestamped, attributable, and protected from alteration.
These mechanisms serve different purposes. Access controls limit what may happen, version control organizes authorized changes, hashes reveal content differences, and audit records help explain what happened.
How digital signatures support integrity
A digital signature uses public key cryptography to bind a cryptographic signature to specific data.
In simplified terms, the signing process calculates a hash of the document and creates a signature using the signer’s private key. Verification uses the corresponding public key to check whether the signature remains valid for that document. If the protected content changes, verification should indicate that the signed data no longer matches.
A digital certificate may help associate the public key with a person, organization, or system. This adds identity context, but the strength of that association depends on how the certificate was issued, managed, and validated.
Digital signatures do not make documents confidential. They also do not prove that every statement in a document is true or that the signer understood the contents. Their technical role is to support integrity and authenticity for the signed data.
Integrity, authenticity, and confidentiality
These concepts overlap, but they answer different questions.
| Concept | Core question | Common supporting controls | What it does not establish by itself |
|---|---|---|---|
| Integrity | Has the document changed from the identified state? | Hashes, digital signatures, version control, protected audit records | Who created it or who was authorized to sign |
| Authenticity | Is the document or signature genuinely associated with the claimed source? | Signer authentication, digital certificates, digital signatures | Whether the document remained private |
| Confidentiality | Was access limited to authorized people? | Encryption, permissions, secure transmission | Whether an authorized person altered the document |
A document can have integrity without confidentiality. For example, a publicly available policy may be unencrypted but protected by a verifiable digital signature. A confidential document can also lack integrity if an authorized user changes it without creating a traceable new version.
Document integrity during signing
Consider a contract sent to two recipients for electronic signature. The workflow identifies the exact file presented to each signer, records relevant signing events, and produces a completed version. A hash or digital signature can later help verify whether that completed file still matches the recorded version.
If someone changes a payment term afterward, the integrity check may fail or the signature status may show that the document was modified. Some document formats and signing configurations allow limited post-signing actions, such as completing approved fields or adding another signature. The effect depends on which content was protected and how the software validates later changes. See can you edit a PDF after signing? for a closer explanation.
A similar principle applies outside contracts. Organizations may use integrity controls to distinguish the approved version of a policy, confirm that an issued invoice has not changed, or preserve the contents of a completed application.
What integrity evidence cannot establish
Document integrity is evidence about the document’s state, not a complete judgment about its legal effect.
An unchanged document may still contain an error, an unauthorized term, or a signature obtained through an unsuitable process. Integrity evidence does not automatically prove identity, consent, authority, capacity, compliance, or enforceability.
The legal significance of a document depends on the applicable jurisdiction, the type of transaction, the parties’ conduct, and any required formalities. Hashes, audit records, and digital signatures may support an evidentiary record, but they do not guarantee a legal outcome. Organizations handling sensitive or regulated documents should obtain advice appropriate to their circumstances.
FAQ
Does a matching hash prove that a document is authentic?
No. A matching hash shows that a file matches the version used to create the reference hash. Authenticity requires additional evidence connecting that version to a trusted source.
Does a digital signature encrypt the document?
Not necessarily. A digital signature supports integrity and authenticity, while encryption protects confidentiality. A document may use either control or both.
Can an authorized edit preserve document integrity?
The edit changes the document relative to its earlier state, but it can become a new controlled version with its own integrity evidence. The revision should be clearly identified and recorded.
Is a scanned signed document the same as the original?
No. A scan is a digital representation of the paper document. It may be useful evidence, but it does not automatically establish the condition, completeness, or custody of the physical original.