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I have PDF files which get created from a scanner. The PDFs only contain images.

Up to now you can't copy+paste the text if you look at the PDF with Acrobat or an other PDF viewer.

Needed features:

  • OCR: read text from the images
  • Annotate the PDF and create a hidden overlay to make text copy and pastable.
  • Processing of one page should not last longer then 20 seconds
  • Command-line and/or API, no GUI needed

Optional:

  • If there is an API, Python bindings would be nice

I only need to support Linux, no other operating system. Open source preferred, but commercial software recommendations are valid answers, too.

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4 Answers 4

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The solution you want can be found at our sister site: how to OCR a pdf file and get the text stored within pdf? Quoting this answer:

Best and easyest way out there is to use pypdfocr it doesn't change the pdf. pypdfocr is a python module link here.

pypdfocr your_document.pdf

At the end you will have another your_document_ocr.pdf the way you want it with searchable text. The app doesn't change the quality of the image. Increases the size of the file a bit by adding the overlay text.

I think the command is pretty easy that it doesn't need any GUI. Maybe installing pypdfocr is a bit more verbose:

sudo dnf -y install tesseract 
pip install pypdfocr

I can't tell about processing time, and certainly you'll need a separate tool to create the annotations – but all your other requirements should be perfectly met:

  • OCR: Yes.
  • open source: Yes.
  • command line, no GUI needed: Yes.
  • Support Linux: Yes.
  • Python bindings: Well, it's plain Python (except for calling to Tesseract).

Alternatively, working the same way, there's another Python module called ocrmypdf. This also uses Tesseract for the OCR process.

A third candidate would be pdfsandwich – but that comes without the Python component.

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I personally use Adobe's Creative Cloud - All Apps
https://www.adobe.com/creativecloud/plans.html

  • Monthly subscription - cancel anytime.

  • OCR - quality depends on the dots per inch scan. Readability and quality of scanned item.

  • Pasteable text - yes.

  • Editable original text - yes.

  • Notation - Yes

Unfortunately I can not answer for the following:

  • Command Line and or API.

From my research Adobe will work on Linux.

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Have a look at Tesseract, open source OCR software.

It comes with a command line program and there are Python bindings as well. Packages available in your Linux distro.

apt-get install tesseract-ocr
#convert pdf to scans.tiff
tesseract scans.tiff out pdf
  • ✓ OCR
  • ✓ searchable PDF output
  • ✓ open source
  • ✓ fast enough (v3 faster than v4 though)
  • ✓ command-line and/or API
  • ✓ works on Linux
  • ✓ python bindings
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  • Unfortunately tesseract can't take a PDF (containing for example 5 scanned pages) and output a PDF with hidden text annotations. At least I could not find a way to do it.
    – guettli
    Commented Jun 6, 2018 at 7:58
  • I think the missing step is that you'd need to first convert the PDF file to a multipage TIFF image, which you then pass as input to tesseract.
    – Edi
    Commented Jun 6, 2018 at 11:14
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This Python3 based tool does have all features: https://pypi.org/project/ocrmypdf/

  • OCR: yes
  • Annotate the PDF and create a hidden overlay to make text copy and pastable: yes
  • Processing of one page should not last longer then 20 seconds: yes
  • Command-line and/or API, no GUI needed: yes
  • If there is an API, Python bindings would be nice: yes
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