Know which digital letter is the original.

The correspondence workflow in practice.

Consider two documents that look nearly identical: the subject and recipient are the same, but one amount or paragraph has changed. File names are unreliable evidence of which document was sent. A stored fingerprint and finalisation record can help answer that question without requiring the user to inspect every page by hand.

Integrity must be presented responsibly. A hash cannot tell a recipient whether an identity was checked, whether a post carrier accepted an envelope or whether the person read it. Those facts need their own evidence and authentication controls.

A practical integrity check begins with the exact file that matters. A customer may have saved several copies of a formal letter in different folders, and a colleague may have converted one into a different PDF format. Two files that look the same on screen can have different bytes and therefore different hashes. The product should explain this behaviour rather than implying that a mismatch always means malicious alteration. The original finalised file and its recorded fingerprint are the correct point of comparison.

For higher-assurance evidence, a signed manifest can associate the relevant file digests with the letter reference and finalisation event. Independent timestamp evidence may add value where the use case warrants it. These controls require careful key management, verified event sources and defined retention; placing a hash on a decorative certificate is not enough. The user-facing report should translate the result into plain language while preserving the technical details for an authorised reviewer.