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LibreOffice OCR: what works on a scanned PDF

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words LibreOffice found, 10-page scan

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OCRmyPDF first: Draw yes, Writer no

LibreOffice has no OCR, so I ran OCRmyPDF first, then opened each PDF in Draw (the default) and Writer.

10 scanned pages, 1,955 words
PDF Opened in Words in order
The scan Draw 0
The scan Writer 0
OCRmyPDF's PDF Draw 1,875
OCRmyPDF's PDF Writer 175

Both got all 2,054 words of the hidden text, in 933 small text boxes. In Writer, the words came out of order.

Draw shows one OCR line a page

On all 10 pages, Draw put one text box in front of the scan, not behind it. That line shows as black text over the page.

Two crops of one line of a book page. Top: the clean scan. Bottom: the same line after Draw, with the OCR text printed in black over the scanned words.
Page 5. Top: the scan. Bottom: the same page from Draw, saved as PDF.

The sandwich renderer did the same. Saved as PDF again, the file kept the stray lines. pdftotext found 1,570 words in order, against 1,855 in OCRmyPDF's own PDF.

Need to edit pages in Draw? Edit first, then OCR. OCRmyPDF stopped on Draw's PDF with TaggedPDFError. With --mode force it found 1,857 in order.

The fix: open the text in Writer

To edit the words, skip the PDF. --sidecar writes OCRmyPDF's text to a file, and Writer opens it. I saved this as pdf2odt.sh and ran sh pdf2odt.sh eng: 

ocrmypdf --jobs 2 --mode force -l "$1" --output-type none --sidecar book.txt book.pdf -
soffice --headless --convert-to odt book.txt

1,875 of 1,955 words, in order

31 s for 10 pages, 2 cores

The document is plain text, with no page images. Each line end became a new paragraph.

German needs a language file

With eng, the 3 German pages lost all 206 umlauts. With deu, OCRmyPDF stopped: Homebrew Tesseract had only eng and osd. My lang.sh copies Tesseract's folder and adds German: 

cp -RL "$(brew --prefix)/share/tessdata" tessdata
curl -sL -o tessdata/deu.traineddata https://github.com/tesseract-ocr/tessdata/raw/main/deu.traineddata

Then I set TESSDATA_PREFIX to that folder and ran sh pdf2odt.sh deu.

193 of 206 umlauts

928 of 972 words in order, two columns

Want headings? Use the Actor

LibreOffice 26.8 opens Markdown in Writer. Our Actor makes Markdown from a file URL: 

curl -s -X POST "https://api.apify.com/v2/acts/brasspage~pdf-ocr-to-markdown/run-sync-get-dataset-items" \
  -H "Authorization: Bearer $APIFY_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"documentUrls": ["https://api.apify.com/v2/key-value-stores/sTnmNrGoSsi7tLQvs/records/anythingllm-mixed-11-pages.pdf"]}' \
  | jq -r '.[].markdown' > mixed.md
soffice --headless --convert-to odt mixed.md

1,874 of 1,955 words, OCRmyPDF 1,875

954 of 972 in order on two columns, OCRmyPDF 928

It read all 13 words of the typed cover page, and Writer kept its headings.

It was slower: 147 s for 11 pages, OCRmyPDF 30 s. It lost one word and one umlaut. It costs $0.006 a page. OCRmyPDF is free and offline.

How I tested it
  • Scan: the 10 pages of OCR in n8n, proofread Wikisource book scans, 1,955 true words. The 11-page file adds the 13-word typed cover page of AnythingLLM OCR.
  • German: the 3 pages of Paperless-ngx OCR, 1,887 words, 206 umlauts. One is a two-column magazine page.
  • Score: I read the text out of each saved file, or with pdftotext for a PDF. Then true words found in order, with the scorer of the tessdata test. German: the scorer of Tesseract German.
  • LibreOffice 26.8.1.1 (Homebrew cask), OCRmyPDF 17.13.0, Homebrew Tesseract 5.5.4, on an arm64 Mac. 2 cores at the lowest priority.
  • The code blocks above are the files that ran. The Actor: two real runs, build 0.1.65.
What I did not test
  • The LibreOffice window. I used soffice --headless, with a fresh profile.
  • LibreOffice extensions, and Windows or Linux.
  • Other output formats, like DOCX.
Sources

Two ways to skip the work

Run it yourself. Our Apify Actor turns scanned PDFs into Markdown, tables included.

Try the Actor

Or send us the scan. Tack, our AI, does the job for $29, up to 50 pages. First page free.

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Questions people ask

Does LibreOffice have OCR?

Not in my test. LibreOffice 26.8.1 opened a 10-page scan as 10 page images with 0 words, in Draw and in Writer.

Why are my OCR words scrambled in Writer?

Writer opened OCRmyPDF's PDF as 933 small text boxes, and only 175 of 1,955 words came out in order. Open the --sidecar text file in Writer instead: 1,875 in order.

My PDF has typed pages too. Which OCRmyPDF mode?

The default mode stopped: page 1 already has text. With --mode skip, redo or force, Draw read all 13 typed words and the same 1,875 scan words.

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