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68 lines
2.4 KiB
Markdown
68 lines
2.4 KiB
Markdown
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---
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layout: docs
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title: Convert PDF Files
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permalink: dev/adr/0015_convert_pdf_files
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---
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# {{ page.title }}
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## Context and Problem Statement
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Some PDFs contain only images (when coming from a scanner) and
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therefore one is not able to click into the pdf and select text for
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copy&paste. Also it is not searchable in a PDF viewer. These are
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really shortcomings that can be fixed, especially when there is
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already OCR build in.
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For images, this works already as tesseract is used to create the PDF
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files. Tesseract creates the files with an additional text layer
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containing the OCRed text.
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## Considered Options
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* [ocrmypdf](https://github.com/jbarlow83/OCRmyPDF) OCRmyPDF adds an
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OCR text layer to scanned PDF files, allowing them to be searched
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### ocrmypdf
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This is a very nice python tool, that uses tesseract to do OCR on each
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page and add the extracted text as a pdf text layer to the page.
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Additionally it creates PDF/A type pdfs, which are great for
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archiving. This fixes exactly the things stated above.
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#### Integration
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Docspell already has this built in for images. When converting images
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to a PDF (which is done early in processing), the process creates a
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text and a PDF file. Docspell then sets the text in this step and the
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text extraction step skips doing its work, if there is already text
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available.
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It would be possible to use the `--sidecar` option with ocrmypdf to
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create a text file of the extracted text with one run, too (exactly
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like it works for tesseract). But for "text" pdfs, ocrmypdf writes
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some info-message into this text file:
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```
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[OCR skipped on page 1] [OCR skipped on page 2]
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```
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Docspell cannot reliably tell, wether this is extracted text or not.
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It would be reqiured to load the pdf and check its contents. This is a
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bit of bad luck, because everything would just work already. So it
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requires a (small) change in the text-extraction step. By default,
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text extraction happens on the source file. For PDFs, text extraction
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should now be run on the converted file, to avoid running OCR twice.
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The converted pdf file is either be a text-pdf in the first place,
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where ocrmypdf would only convert it to a PDF/A file; or it may be a
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converted file containing the OCR-ed text as a pdf layer. If ocrmypdf
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is disabled, the converted file and the source file are the same for
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PDFs.
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## Decision Outcome
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Add ocrmypdf as an optional conversion from PDF to PDF. Ocrmypdf is
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distributed under the GPL-3 license.
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