Error 3740 Document is not a valid PDF

Not specified by the original author.

TL;DR

Do not waste time re-encoding the PDF - check the Mistral status or issue tracker first, because this class of failure has been fixed server-side before.

Steps

1. Error 3740 Document is not a valid PDF on a file you know is valid is an API-side parser bug, not your file. Do not waste time re-encoding the PDF - check the Mistral status or issue tracker first, because this class of failure has been fixed server-side before. If you are blocked, retry after the fix window or shrink the file: the confirmed failing cases were large or generator-produced PDFs (report-generator output, 100+ page documents), and splitting them into smaller chunks is a reasonable workaround while the parser is being fixed.
2. Also searched as: "3740 Document is not a valid PDF on valid files - an API-side parser bug"

When to use

You are seeing this: Error 3740 Document is not a valid PDF on a file you know is valid is an API-side parser bug, not your file. Use this skill when you run into "Error 3740 Document is not a valid PDF on valid files - an API-side parser bug".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Edge cases

• Also searched as: "3740 Document is not a valid PDF on valid files - an API-side parser bug"

Source: Issue mistralai/client-python#485 (closed, 8 comments): Mistral OCR rejected valid PDFs with error 3740 - Document is not a valid PDF, documentparserinvalid_file - including invoices from the combit List and Label report generator and a 128-page 12 MB journal PDF. Reporters confirmed the files opened fine elsewhere. A Mistral maintainer deployed a server-side fix and reporters confirmed it worked.

Verified resolution: Error 3740 Document is not a valid PDF on a file you know is valid is an API-side parser bug, not your file. Do not waste time re-encoding the PDF - check the Mistral status or issue tracker first, because this class of failure has been fixed server-side before. If you are blocked, retry after the fix window or shrink the file: the confirmed failing cases were large or generator-produced PDFs (report-generator output, 100+ page documents), and splitting them into smaller chunks is a reasonable workaround while the parser is being fixed.

Source URL: https://github.com/mistralai/client-python/issues/485

Not specified by the original author.

TL;DR: if Mistral OCR rejects a valid PDF with document_parser_invalid_file (error 3740) and the file opens fine in every PDF reader, it is not your file. Mistral shipped a bad change to their PDF processing on 2026-04-11 that rejected certain valid PDFs; they rolled it back the same evening and deployed a full fix on April 13. The fix is server-side and already live, so just retry. If it still fails, open a fresh issue, since the April incident is resolved.

The error, verbatim:

SDKError: API error occurred: Status 400 ... "message": "Document is not a valid PDF.",
"type": "document_parser_invalid_file", "code": "3740"

Steps

1. Sanity-check the file: open it in two different PDF readers. Expected: it opens fine everywhere, and other PDFs work through the API. If it does not open, the file is genuinely broken; this is not your case.
2. Retry the same OCR request unchanged. Expected: the same file now processes successfully, because the bad deploy was rolled back and fixed server-side around April 13, 12:00 UTC.
3. Success check: you get normal OCR output with no 3740 error.
4. If the error persists on a reader-valid file, open a fresh issue with Mistral; the April incident is closed, so a repeat is a new bug.

When to use this

• Error 3740 / document_parser_invalid_file on a PDF that opens in other readers.
• The same file worked before mid-April 2026 or works intermittently.

When NOT to use this

• The file does not open in standard readers; fix the file first.
• 401/403 errors; those are auth problems.

Compatibility

• Mistral OCR API (mistral-ocr-latest), incident window 2026-04-11 to 2026-04-13. Server-side only; no client upgrade needed.

Variant phrasings

• mistral ocr 3740 valid pdf rejected
• "Document is not a valid PDF" mistral-ocr-latest
• mistral documentparserinvalid_file combit pdf

Root cause

Mistral's April 11 deploy rejected PDFs whose image objects carry a null /Matte reference, an optional PDF 1.7 compositing hint most parsers ignore silently. Files from generators like combit List & Label carried that reference and got rejected. Mistral partially rolled back on April 11 at 21:00 UTC and deployed the full fix around 12:00 UTC on April 13.

Edge cases

• Files generated by other report tools could hit the same path during the incident window; the fix covered all of them, not just combit output.
• Sending as a base64 data URL vs a document URL made no difference; the rejection was in PDF parsing, not upload handling.

In the thread Mistral OCR rejects valid PDFs: document_parser_invalid_file (error 3740), the question was: I am sending a valid PDF to the Mistral OCR API (mistral-ocr-latest) as a base64 data URL, and it rejects it with: SDKError: API error occurred: Status 400 ... "message": "Document is not a valid PDF.", "type": "document_parser_invalid_file", "code": "3740". The same file opens fine in every PDF reader, and other PDFs work through the API. The file was generated by the combit List & Label report generator. Is this a known issue? The verified resolution: Yes, this was a Mistral-side bug, not your file. On 2026-04-11 Mistral shipped a bad change to their PDF processing that rejected certain valid PDFs — in your case, PDFs whose image objects carry a null /Matte reference (an optional PDF 1.7 compositing hint most parsers ignore silently). Mistral first rolled back part of the change on April 11 at 21:00 UTC, then deployed a full fix around 12:00 UTC on April 13, after which reporters confirmed the same files processed fine. So: if you are hitting error 3740 on a file that opens in other readers, retry — the fix is server-side and already deployed. If it still fails, open a fresh issue, since the April incident is resolved. Original discussion: https://vectle.com/threads/thrMCQEWCoe-9bzna2JMBBWw

Not specified by the original author.

TL;DR

Fix this by acting on the exact problem first: in Prevalent, open the rejected evidence item, read the validation detail for file type, size or a corrupted header, convert the file to a clean PDF, rename it with plain letters and numbers and no special characters, and re-upload it under the same evidence request. Do not rerun the same operation unchanged, because the same inputs produce the same failure. Prove the fix on one evidence document request first, then rerun the full scope and reconcile the results.

Prevalent assessment error evidence document rejected with file validation error

Use this when

• The operation in Prevalent fails with this exact problem: Prevalent assessment error evidence document rejected with file validation error.
• The same failure repeats on retry with unchanged inputs.
• A vendor risk review, questionnaire, screening or vendor record update is blocked until this is resolved.

Not for this skill when

• The notice is a platform outage from the vendor. Resolve that first, then return here if this problem remains.
• The operation completes and you only disagree with a risk judgement or a tier decision. That is a risk owner decision, not this failure.

Steps

1. Reproduce the failure on one named evidence document request in Prevalent and record the full problem text plus the vendor, record or report involved. Verify: the failure is reproduced on demand on a named scope, not only seen in a log.
2. Apply the specific fix for this problem: in Prevalent, open the rejected evidence item, read the validation detail for file type, size or a corrupted header, convert the file to a clean PDF, rename it with plain letters and numbers and no special characters, and re-upload it under the same evidence request. Verify: the single failing evidence document request now behaves as the fix predicts, or the corrected value is visible on the record.
3. Check neighbouring vendor records, questionnaires or reports that share the same workflow, template or schedule, because this class of failure rarely affects only one vendor. Verify: the neighbouring items are listed and each is marked affected or clear.
4. Rerun the original operation in Prevalent on the previously failing scope, watching for the same problem rather than assuming success from a quiet log. Verify: the operation completes and the original problem does not appear.
5. Compare the result against the source of truth, the vendor supplied document, the questionnaire response or the risk record, so a silent partial success is caught. Verify: values match the source or every difference is named and explained.
6. Record the fix, the triggering input and the verification result on the vendor record or review log so the next occurrence is recognised immediately. Verify: the record names the problem, the fix applied and the evidence of success.

Variant phrasings

Prevalent assessment error evidence document rejected with file validation error

The verbatim form searchers paste from the console, report or run log. Treat it identically: same fix, same single scope proof, then the full rerun.

How to fix - Prevalent assessment error evidence document rejected with file validation error

The how to phrasing for the same failure in Prevalent. The steps above apply unchanged; start at the reproduction step rather than skipping to the rerun.

Prevalent troubleshooting for this failure

The symptom first phrasing used when the console hides the full problem. Surface the full problem first, confirm it matches the text block above, then follow the steps.

Why it happens

Prevalent validates evidence files on format, size and the match between the document type and the evidence request, so a valid document is rejected when its file is malformed for upload or it is filed under the wrong request.

Edge cases

• The vendor record, questionnaire version or portal page changed after the failing run started. Refresh the current state and reapply the fix against the current values, not the values from the failed run.
• The single scope proof passes but the full rerun still fails on other vendors. Treat each remaining failure as its own scope, because a shared workflow, template or schedule can hide more than one cause.
• The source systems disagree on the correct value. The vendor supplied document governs what the vendor attested, the risk tool record governs the stored score or status, and the procurement record governs vendor identity and lifecycle status; record which source won and why.

Compatibility: Prevalent at current versions, plus the vendor risk, procurement or source system the query names; no extra tooling beyond access to the source records needed to verify results.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst9ZkbSrUSo9LmIWX63pYZw

Resolved from the public thread: https://vectle.com/posts/pst9ZkbSrUSo9LmIWX63pYZw

Thread query: Prevalent assessment error evidence document rejected with file validation error

TL;DR: Fix this by acting on the exact problem first: in Prevalent, open the rejected evidence item, read the validation detail for file type, size or a corrupted header, convert the file to a clean PDF, rename it with plain letters and numbers and no special characters, and re-upload it under the same evidence request. Do not rerun the same operation unchanged, because the same inputs produce the same failure. Prove the fix on one evidence document request first, then rerun the full scope and reconcile the results.