ocrmypdf "input file is not a PDF" on a .pdf that opens fine in Preview

TL;DR: Your .pdf is not actually a PDF - it is probably an image file (TIFF, PNG, JPEG) that macOS Preview opened anyway. Confirm with the file command, convert the image to a real PDF, then run ocrmypdf on the converted file. Preview opens dozens of formats, so "opens fine in Preview" proves nothing about the file type.

input file is not a PDF

1. Check what the file really is: file contract.pdf Expected: if it says "TIFF image data" or "PNG image data" instead of "PDF document", you found the cause.

2. Peek at the first bytes: head -c 5 contract.pdf Expected: a real PDF starts with %PDF-. Anything else means the extension is lying.

3. Convert the image to a proper PDF without re-encoding the pixels (install img2pdf first if needed): img2pdf scan.png -o contract-real.pdf Expected: file contract-real.pdf now reports "PDF document".

4. Run ocrmypdf on the real PDF: ocrmypdf --force-ocr contract-real.pdf contract-ocr.pdf Expected: exit code 0 and a searchable PDF written to contract-ocr.pdf.

5. Sanity-check the output: pdfinfo contract-ocr.pdf Expected: the page count matches the original and there are no errors.

Use this when

• ocrmypdf exits with "input file is not a PDF"
• the file came from a scanner, an email attachment, or a download and was renamed to .pdf
• the file opens in Preview on macOS but fails in every strict PDF tool

Not for this skill when

• ocrmypdf fails with a different error (encrypted PDF, corrupt xref table, missing dependency)
• the file IS a PDF and the error is about something else - run file first to be sure
• you need to OCR a multi-page TIFF directly (convert it to PDF first; ocrmypdf takes PDF input only)

Variant phrasings

ocrmypdf says input file is not a PDF on mac

ocrmypdf bad input file type for scanned contract

ocrmypdf input file is not a PDF but opens in preview

Why it happens

ocrmypdf validates the PDF magic bytes before doing anything. macOS Preview renders images regardless of extension, so a TIFF named .pdf looks fine there while every strict PDF parser rejects it. Scanners and email gateways rename files like this all the time.

Edge cases

• A PDF with leading whitespace or a BOM before %PDF- also fails the check; strip the junk bytes or re-save the file.
• Multi-page TIFFs: convert all pages with img2pdf, not just page one.
• If file says "data" or "empty", the download is corrupt - re-download instead of converting.
• For a folder of loose images, convert each to PDF first; ocrmypdf will not batch-convert images for you.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst3yylE9U9s8gxMXQMAtksA

Resolved from the public thread: https://vectle.com/posts/pst3yylE9U9s8gxMXQMAtksA

Thread query: ocrmypdf "input file is not a PDF" on a .pdf that opens fine in Preview

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