TL;DR: The completion certificate fails validation because the download is truncated or the document changed after signing. Re-download the file, open it in a different PDF reader to rule out viewer quirks, and compare against Concord's stored record. If the hash genuinely mismatches, the document was altered post-signature - request a fresh certificate from Concord support.

```text
e-signature certificate invalid
```

1. Re-download the audit trail or certificate from Concord and check the file size.
   Expected: a complete, non-zero file that opens as a PDF.
2. Open it in a different PDF reader (if you used a browser viewer, try a desktop reader).
   Expected: if the second reader validates it, the first reader's signature handling was the problem.
3. Check whether anyone edited, re-saved, or re-exported the document after signing.
   Expected: no post-signing changes - any edit invalidates the certificate hash.
4. Compare the document against Concord's stored completion record.
   Expected: hashes match; if they do not, the file you hold is not the signed one.
5. If the mismatch persists on a fresh download, contact Concord support for a reissued certificate.
   Expected: support confirms the record or reissues the certificate.

## Use this when
- downloading the Concord audit trail or completion certificate shows an invalid signature
- the agreement itself shows as signed and complete in Concord
- you need the certificate for an audit or filing

## Not for this skill when
- the download fails entirely (fix the download, not the certificate)
- the agreement is still in progress (there is no completion certificate yet)
- the error is about a different document's signature

## Variant phrasings
### concord e-signature certificate invalid download
### concord audit trail signature validation failed
### concord completion certificate not valid

## Why it happens
The certificate binds a cryptographic hash of the exact bytes that were signed. A truncated download changes the bytes; so does any post-signing edit, even re-saving without visible changes. Validators then correctly report the signature as invalid - the math no longer matches.

## Edge cases
- Browser PDF viewers sometimes validate embedded signatures poorly; a desktop reader is the tiebreaker.
- The audit trail and the completion certificate are separate downloads - make sure you are validating the right file.
- Timestamp authority hiccups can cause transient validation failures; re-download later before escalating.
- Never "fix" an invalid certificate by re-signing quietly - that creates a new legal event.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_ubF7HfKXz3r_cETtPFcuAg