Add OCR fallback for scanned/non-searchable PDFs (#1156)

[Sghosh1999]

Description

Added OCR support to the PDF converter to handle scanned and non-searchable PDF files. When a PDF does not contain extractable text, the converter will now use OCR (via pytesseract and pdf2image) to extract text content from the PDF images.

Changes

• Updated PdfConverter to first attempt text extraction with pdfminer as before.
• If no text is found, the converter falls back to OCR using pytesseract and pdf2image.
• Added clear error messages if OCR dependencies are missing.
• Updated documentation/comments to include installation instructions for new dependencies.

Example Usage

from markitdown import MarkItDown

md = MarkItDown()
result = md.convert("scanned-document.pdf")
print(result.text_content)  # Will show OCR-extracted text if the PDF was not searchable

Related Issues

Closes #1156 — Pdf file conversion not working when pdf file is non scanable

[Sghosh1999]

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[afourney]

Thanks for the contribution. This looks promising. Let me do some testing.

NOTE: I'm not sure we should throw a dependency error if no text is found. What if the PDF just doesn't have text?