Do a screenshot or an exported PDF work as evidence?

They work as a hint, but they're weak: anyone can edit an image or regenerate a PDF, and neither on its own shows who produced it or when. What gives it strength isn't the format —it's being able to prove integrity, origin and date in a verifiable way.

Is storing the file's hash enough for evidentiary weight?

No. The hash proves integrity —that two copies are identical— but it says nothing about who produced it or when, and on its own it doesn't stop someone replacing both file and hash. It's one pillar of three, not the whole proof.

Who ultimately decides whether an electronic document is valid evidence?

Whoever resolves the matter —a judge, an arbitrator, an auditor— under the applicable rules. The technique doesn't replace that judgement: it supports it, giving the decider verifiable reasons to trust that the document is intact, authentic and dated.

What gives an electronic document evidentiary weight

An electronic document —a PDF, an email, a log, a contract signed on screen— isn't evidence just because it exists. It becomes evidence when it survives an uncomfortable question from someone who doesn't trust you: “how do I know this is the same file that was created, that it was produced by who you say, and that it existed when you say?”. Answering that verifiably is what we call evidentiary weight, and it isn't declared —it's built from the origin.

There are three pillars, and it pays not to confuse them:

Integrity — the document wasn't altered since it was fixed. Not one byte.
Authenticity — it can be attributed to who claims to have produced it, not to anyone.
Trustworthy date — it existed at a specific moment, and that moment wasn't set by the interested party at will.

When the three hold together, a fourth property emerges —the one that really matters in a dispute: non-repudiation, the difficulty for the signer to later deny they signed.

How the technique supports each pillar

Cryptography doesn't “make” a document legal —the law decides that— but it gives whoever judges concrete reasons to trust.

Integrity: the hash. A hash function reduces the whole file to a short fingerprint. Change one byte and the fingerprint changes entirely. If you store the fingerprint when the document is fixed, anyone can recompute it later and confirm the file wasn't touched. It's cheap and powerful, but it proves only integrity: not who made it, nor when.

Authenticity: the digital signature. Here public-key cryptography comes in. The signer holds a private key they never share; the world has their public key. Signing applies the private key to the document's hash; verifying checks, with the public key, that only that private key could have produced the signature. That binds the document to a specific key —and, if trust in the key is properly set up, to a person.

Date: timestamping. A trusted third party —or a source no one controls at will— certifies that the document's hash existed at a given instant. Without this, the date is whatever the clock of the person presenting the file says, which proves nothing to a skeptic.

The link the machine doesn't close on its own

A digital signature proves a document corresponds to a key. That the key belongs to a person is a different, trust problem, solved by the infrastructure around it: a PKI, a certificate issued by an authority, or the process by which you verified the signer's identity. Confusing “the signature verifies” with “the signature is so-and-so's” is the most common mistake, and it's exactly where technically sound evidence falls apart in practice.

What is NOT enough

The hash alone: integrity without origin or date.
A screenshot or a PDF “signed” with an image: they prove neither integrity nor origin; a signature image is copy-pasted.
“Trust my log”: a log the custodian can edit is not evidence before a third party, however complete.

What the software must do

The design consequence is simple: a system meant to produce defensible evidence doesn't just store the datum —it records the chain. It fixes the hash on receiving the document, signs it, timestamps it, and keeps who touched it and when —so that this record, too, can't be rewritten unnoticed. Evidentiary weight isn't a box ticked at the end: it's a property the system has to build from the first moment, or it doesn't have it.

Whoever decides if a document serves as evidence is always a person with the authority to do so, under the applicable rules. The technique doesn't take that place. What it does —and it's no small thing— is give that person verifiable reasons, not just your word, to believe the document is intact, authentic and dated.