scanned PDF with no text layer: extraction returns empty

TL;DR

A scanned PDF with no text layer returns empty from text extractors, which looks like a blank invoice. Detect it fast: if text extraction yields fewer than a threshold of characters, classify the PDF as image-only and send it to the OCR path automatically. Never let an empty extraction proceed as a zero-amount invoice.

Error

extract_text() returned 0 characters for invoice_1042.pdf

Steps

1. Attempt text extraction and count the characters returned.

Expected: A character count, often near zero for scans.

1. If below threshold (e.g. 50 characters), mark the PDF as image-only.

Expected: Correct routing decision.

1. Render each page at 300 DPI and run OCR.

Expected: Actual text content.

1. Verify the OCR output contains invoice-like fields (total, date, vendor).

Expected: Confirmation this is an invoice, not a blank scan.

1. If OCR also returns nothing, flag as unscannable and request a resend.

Expected: The vendor provides a readable copy.

When to use

• PDF text extraction returns empty
• Ingesting email attachments of unknown type
• Building the intake classifier

When not to use

• Digital PDFs with embedded text
• OCR accuracy problems on readable scans
• Password-protected PDFs

Compatibility

PyMuPDF/pdfplumber for detection; Tesseract, Textract, Document AI for the OCR path.

Variant phrasings

PDF has no text layer

scanned invoice returns empty text

image-only PDF detection

Root cause

Scanners produce images wrapped in a PDF container with no text objects. Text extractors only read text objects, so they return nothing; only a raster-plus-OCR path can read the content.

Edge cases

• Some PDFs have a text layer only on page 1; check per page, not per document
• Password-protected PDFs also return empty; detect encryption first
• Fax-quality scans may need preprocessing before OCR succeeds

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_2Im6aoGoO5TABz9nBjQcSA