Create searchable PDF files using OCR from scanned PDFs in bulk

Question

The goal is to automatically convert all scanned documents into searchable PDF files instead of just images. The scanned documents are automatically uploaded by the scanner to a share on a Linux server as PDF files.

The software should be able to monitor the folder and automatically OCR the scanned documents and add the recognized text to the PDF file to make it searchable. It should also be able to handle multi-page PDFs well.

Requirements:

• Linux
• Work automatically in the background without any additional manual steps
• Being able to add the OCRed text back into the PDF in the proper way (so that desktop search engines will be able to index it)
• Able to handle multi-page PDF files

Answer 1

OCRmyPDF
Website: https://github.com/jbarlow83/OCRmyPDF
License: MIT License

OCRmyPDF adds an OCR text layer to scanned PDF files, allowing them to be searched

Answer 2

pypdfocr
Website: https://pypi.python.org/pypi/pypdfocr
License: ASL 2.0

I wrote a pretty simple way to search all pdfs that are not already OCRed and OCR them.

I noticed if a pdf file doesn't have any font it is usually not searchable. So knowing this we can use pdffonts.

First 2 lines of the pdffonts are the table header, so when a file is searchable has more than two line output, knowing this we can create:

gedit check_pdf_searchable.sh

then paste this

#!/bin/bash 
#set -vx
if ((`pdffonts "$1" | wc -l` < 3 )); then
echo $1
pypdfocr "$1"
fi

then make it executable

chmod +x check_pdf_searchable.sh

then list all non-searchable pdfs in the directory:

ls -1 ./*.pdf | xargs -L1 -I {} ./check_pdf_searchable.sh {}

or in the directory and its subdirectories:

tree -fai . | grep -P ".pdf$" | xargs -L1 -I {} ./check_pdf_searchable.sh {}