Hocr

C# Library for converting PDF files to Searchable PDF Files

• Need to batch convert 100 of scan PDF's to Searchable PFS's?
• Don't want to pay thousands of dollars for a component?

I have personally tested this library with over 110 thousand PDFs. Beyond a few fringe cases the code has performed as it was designed.. I was able to process 110k pdfs (Some hundreds of pages) over a 3 day period using 5 servers.

Internally, Hocr uses Tesseract, GhostScript, iTextSharp and the HtmlAgilityPack. Please check the licensing for each nuget to make sure you are in compliance.

This library IS THREADSAFE so you can process multiple PDF's at the same time in different threads, you do not need to process them one at a time.

Installation

This project requires the GhostScript Windows x64 executable downloaded for free from here: https://ghostscript.com/releases/gsdnld.html

The GhostScript executable is also required to be installed on all client computers that will run your program and it must be installed in the same path as you've put into your code. During install, keep note of installation directory and modify Program.cs to reflect its location "gswin64c.exe". For example:

PdfCompressorSettings _PdfSettings = new PdfCompressorSettings
{
    PdfCompatibilityLevel = PdfCompatibilityLevel.Acrobat_7_1_7,
    WriteTextMode = WriteTextMode.Word,
    Dpi = 400,
    ImageType = PdfImageType.Tif,
    ImageQuality = 100,
    CompressFinalPdf = true,
    DistillerMode = dPdfSettings.prepress,
    DistillerOptions = string.Join(" ", _DistillerOptions.ToArray())
};
string _GhostScriptPath = @"C:\Program Files\gs\gs10.02.0\bin\gswin64c.exe";

// In example code: private static PdfCompressor _comp;
_comp = new PdfCompressor(_GhostScriptPath, _PdfSettings);

Use Hocr!

Example Usage:

using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
using Hocr.Enums;
using Hocr.Pdf;

namespace Hocr.Cmd
{
    internal class Program
    {
        private static bool _running = true;

        private static int _fileCounter = 3;

        private static PdfCompressor _comp;

        public static void Example(byte[] data, string outfile)
        {
            Tuple<byte[], string> odata = _comp.CreateSearchablePdf(data, new PdfMeta
            {
                Author = "Vince",
                KeyWords = string.Empty,
                Subject = string.Empty,
                Title = string.Empty
            });
            File.WriteAllBytes(outfile, odata.Item1);
            Console.WriteLine("OCR BODY: " + odata.Item2);
            Console.WriteLine("Finished " + outfile);
            _fileCounter = _fileCounter - 1;
            if (_fileCounter == 0)
                Environment.Exit(0);
        }

        private static void Main(string[] args)
        {
            List<string> distillerOptions = new List<string>
            {
                "-dSubsetFonts=true",
                "-dCompressFonts=true",
                "-sProcessColorModel=DeviceRGB",
                "-sColorConversionStrategy=sRGB",
                "-sColorConversionStrategyForImages=sRGB",
                "-dConvertCMYKImagesToRGB=true",
                "-dDetectDuplicateImages=true",
                "-dDownsampleColorImages=false",
                "-dDownsampleGrayImages=false",
                "-dDownsampleMonoImages=false",
                "-dColorImageResolution=265",
                "-dGrayImageResolution=265",
                "-dMonoImageResolution=265",
                "-dDoThumbnails=false",
                "-dCreateJobTicket=false",
                "-dPreserveEPSInfo=false",
                "-dPreserveOPIComments=false",
                "-dPreserveOverprintSettings=false",
                "-dUCRandBGInfo=/Remove"
            };


            PdfCompressorSettings pdfSettings = new PdfCompressorSettings
            {
                PdfCompatibilityLevel = PdfCompatibilityLevel.Acrobat_7_1_6,
                WriteTextMode = WriteTextMode.Word,
                Dpi = 400,
                ImageType = PdfImageType.Tif,
                ImageQuality = 100,
                CompressFinalPdf = true,
                DistillerMode = dPdfSettings.prepress,
                DistillerOptions = string.Join(" ", distillerOptions.ToArray())
            };

            // May need explicit location of GhostScript executable. See Installation instructions above.
            _comp = new PdfCompressor(pdfSettings);
            _comp.OnExceptionOccurred += Compressor_OnExceptionOccurred;
            _comp.OnCompressorEvent += _comp_OnCompressorEvent;


            byte[] data = File.ReadAllBytes(@"Test1.pdf");
            byte[] data1 = File.ReadAllBytes(@"Test2.pdf");
            byte[] data2 = File.ReadAllBytes(@"Test3.pdf");

            new Thread(()=>
            {
                Console.WriteLine("Started Test 1");
                Example(data, @"Test1_ocr.pdf");
            }).Start();

            new Thread(() =>
            {
                Console.WriteLine("Started Test 2");
                Example(data1, @"Test2_ocr.pdf");
            }).Start();

            new Thread(() =>
            {
                Console.WriteLine("Started Test 3");
                Example(data2, @"Test3_ocr.pdf");
            }).Start();

            int counter = 0;
            while (_running)
            {
                Thread.Sleep(1000);
                Console.WriteLine("Working...." + counter);
                counter++;
            }

            Console.WriteLine("Finished!");
            Console.ReadLine();
        }

        private static void _comp_OnCompressorEvent(string msg) { Console.WriteLine(msg); }

        private static void Compressor_OnExceptionOccurred(PdfCompressor c, Exception x)
        {
            Console.WriteLine("Exception Occured! ");
            Console.WriteLine(x.Message);
            Console.WriteLine(x.StackTrace);
            _running = false;
        }
    }
}

Special Thanks to Koolprasadd for his original article at: https://tech.io/playgrounds/10058/scanned-pdf-to-ocr-textsearchable-pdf-using-c