How strongly this file proves, on its own, who signed it and that it has not changed — and how long it will keep proving it, without the signing platform.
Three questions in strict order: integrity (has it changed?), then trust (does the identity chain to a recognised trust regime?), then durability (will it still verify years from now without anyone's help?). This is a ladder of necessary conditions, not a points total — a file receives the highest grade whose conditions it meets in full, and one failed gate caps it regardless of everything else.
All of the following:
The supplier went further than the standard asks.
All of the following:
This is what a properly signed document looks like. It proves who signed it, when, and that nothing has changed — on its own, offline, without the platform that made it.
All of the following:
An independent third party has proven when this was signed, and it will keep verifying for years.
All of the following:
Verifies today. There is no independent proof of when it was signed, and once the signing certificate expires or its revocation data goes offline, it may stop verifying entirely.
All of the following:
You can prove this file has not changed. You cannot prove who signed it. The result also states the grade the file’s own construction would reach with a certificate from a recognised provider — B or C — so a well-built document on a private root is not confused with a self-signed PDF.
All of the following:
Something was signed. This file cannot prove it. The proof sits with the signing platform, not with you. Nothing here is wrong — it is simply not self-proving.
Any one of the following:
This document does not prove what it claims. Do not rely on it without going back to the source.
No letter is issued when there is no signature and no evidence package to assess, or the file cannot be read. This is never shown as F. F means we checked and the document failed; absence of proof is a different statement from disproof.
Tindom validates against every trust source it carries and names the one that vouched for each document, rather than refusing documents that sit outside a preferred list. What differs between regimes is not whether we check them — it is what a positive result legally means, and that is what sets the ceiling.
| Regime | What it is | Legal weight | Ceiling |
|---|---|---|---|
| EU/EEA qualified | Member-state trusted lists under eIDAS Article 22, where the service is granted for qualified certificates. Published by each member state, aggregated by the European Commission. | Qualified signatures have the legal effect of a handwritten signature (eIDAS Article 25(2)); qualified seals carry a presumption of integrity and origin (Article 35(2)). Advanced signatures and seals — including on qualified certificates — carry neither. | A+ |
| Recognised third country | Trusted lists of countries holding an eIDAS Article 14 mutual-recognition agreement — currently Ukraine and Moldova. | Legally equivalent to EU-qualified, by agreement. | A+ |
| EU/EEA non-qualified | On a member-state trusted list, but the service is not granted for qualified certificates. | Supervised; no presumption. | B |
| National regulated | A national trusted list operating outside eIDAS recognition — the Swiss list (ZertES, Swiss Accreditation Service) and the UK list (Information Commissioner's Office). Real supervision, real audit, no EU mutual recognition. | Regulated nationally; no eIDAS presumption. | B |
| Commercial programme | The Adobe Approved Trust List — around 300 certificate authorities admitted under Adobe's published technical requirements and independent audit. This is what makes Adobe Acrobat show a green tick. | Contractual, not statutory; no presumption. | B |
| Not recognised | Chains to no list we carry: self-signed, a private certificate authority, or an unknown issuer. | None. | D |
This list is closed and published, so A+ is achievable rather than a matter of taste. A document needs everything required for A, plus the conditions listed under A+, plus at least one of these:
A document's grade is the lowest of its signatures' grades — a contract is only as good as its weakest party's proof. Each signature also carries its own grade, so the roll-up is never opaque.
A grade is never shown as a bare letter. It always appears with the assurance level, the ETSI form, and the trust regime that vouched for it — the letter carries the legibility, the rest carries the defensibility.
A PDF sealed by an e-signing platform, validated by Tindom. It clears every gate up to the top of the ladder and is then held at B by two separate things — which is the ordinary case, not a failure.
Grade B. Trusted and time-anchored, and it will keep verifying for years — but two separate things stand between it and A, and either one alone would be enough to hold it there. Both are configuration changes on the signing platform's side, not re-architecture.
The scale is only useful if it says what to change. Each entry below is a ceiling a document can hit, what it means, and what would move it up.
Timestamped, but the file does not carry what is needed to verify it on its own later (B-T).
Embed the certificate chain and revocation data at signing time — B-T becomes B-LT. Usually a setting in the signing platform.
The signature alone, with no independent proof of when it was made (B-B).
Add a timestamp from a trusted timestamping authority at signing — B-B becomes B-T, and the document stops depending on a claimed signing time.
An advanced signature or seal, possibly on a qualified certificate, but not a qualified signature or seal in the eIDAS sense.
Issue on a qualified certificate held on a qualified signature creation device (QSCD). This is a change of product with the trust service provider, not a file-format change.
Self-contained, but without archive timestamps the proof cannot be refreshed as cryptographic algorithms age (B-LT).
Apply an archive timestamp — B-LT becomes B-LTA, and the evidence outlives both the certificate and the algorithms in use today.
The certificate chains to nothing we recognise — self-signed, a private authority, or an unknown issuer.
Sign with a certificate from a provider on one of the trust lists above. An internal certificate authority cannot reach beyond D, however well run.
The file records that signing happened, but carries no cryptographic signature we can check.
Embed a real signature in the document itself (PAdES for PDFs) rather than keeping the proof on the platform. This is the single largest step available — it moves a document from E to a graded rung.
Something was added to the file after signing that changes what the document shows, or that the validation engine cannot classify — or the signature covers only part of the content.
Sign the whole document, and make any later change as a new signed revision. Adding validation data, timestamps or further signatures is fine; editing content after signing is not.
The certificate chains to a list whose ceiling is B — a non-qualified EU/EEA service, a national list outside eIDAS recognition, or the Adobe Approved Trust List.
Sign with a qualified certificate from a provider on an EU/EEA Trusted List. The file format is not the limit here; the trust regime is.
The signature is intact and trusted, but the validation engine could not reach a definitive pass — for example because revocation status or a certificate in the chain could not be confirmed.
Embed the full certificate chain and revocation data at signing (B-LT), so the result does not depend on what can be fetched at validation time.
A trusted signature in a form outside the ETSI baseline profiles, so its long-term durability cannot be assessed against them.
Produce signatures to an ETSI baseline profile — PAdES for PDFs, XAdES, CAdES or JAdES otherwise.
A signature is present, but whether the signed content is intact could not be determined.
Check that the file is the original signed version and has not been converted or re-saved after signing.
Meets the ETSI standard in full, but something added after signing changes what the document shows or cannot be classified.
Make later changes as new signed revisions rather than edits to a signed file.
The ETSI standard is met in full, including archive timestamps. A+ needs one more thing from the closed list above.
Add one of the listed markers — for example, embed a complete machine-readable evidence package in the file.
The published text and the grading code now say the same thing. (1) Signature scope: validation data, timestamps and further signatures added after signing no longer count as content outside the signature — this is how PAdES B-LT and B-LTA are built, and under 0.1.0 it held every such PDF at B. (2) The A+ condition "no post-signing modification" now means no material change, for the same reason. (3) A multi-signature document now reaches A+ only if every signature meets A in full; before, the result could depend on signature order. (4) The B and C criteria list every reason a document lands there, and B requires a timestamp rather than a qualified one — the qualification of the timestamp was never checked. (5) A D now states the grade the file’s own construction would reach with a recognised certificate. (6) Corrected the legal weight of the EU/EEA qualified regime. Released as 0.2.0 because the scale is still pre-release; under the published policy the change is major, since one grade can go down.