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How to Read PDFs

by Chaknith Bin

PDF stands for "Portable Document Format." It is a file format developed by Adobe that preserves the fonts, images, graphics, and layout of any source document, regardless of the application and platform used to create it. PDF files are typically used for sharing and viewing documents in a consistent format, regardless of the software or hardware used to open it. IronOcr handles various versions of PDF document with ease.

How to Read PDFs

  1. Download a C# library for reading PDFs
  2. Prepare the PDF document for reading
  3. Construct the OcrPdfInput object with PDF file path
  4. Employ the Read method to perform OCR on the imported PDF
  5. Read specific pages by providing the page indices list


C# NuGet Library for OCR

Install with NuGet

Install-Package IronOcr
nuget.org/packages/IronOcr/
or
C# OCR DLL

Download DLL

Download DLL

Manually install into your project

Read PDF Example

Begin by instantiating the IronTesseract class to perform OCR. Then, utilize a 'using' statement to create an OcrPdfInput object, passing the PDF file path to it. Finally, perform OCR using the Read method.

:path=/static-assets/ocr/content-code-examples/how-to/input-pdfs-read-pdf.cs
using IronOcr;

// Instantiate IronTesseract
IronTesseract ocrTesseract = new IronTesseract();

// Add PDF
using var pdfInput = new OcrPdfInput("Potter.pdf");
// Perform OCR
OcrResult ocrResult = ocrTesseract.Read(pdfInput);
Imports IronOcr

' Instantiate IronTesseract
Private ocrTesseract As New IronTesseract()

' Add PDF
Private pdfInput = New OcrPdfInput("Potter.pdf")
' Perform OCR
Private ocrResult As OcrResult = ocrTesseract.Read(pdfInput)
VB   C#
Read PDF file

In most cases, there's no need to specify the DPI property. However, providing a high DPI number in the constructing of OcrPdfInput can enhance reading accuracy.

Read PDF Pages Example

When reading specific pages from a PDF document, the user can specify the page index number for import. To do this, pass the list of page indices to the PageIndices parameter when constructing the OcrPdfInput. Keep in mind that page indices use zero-based numbering.

:path=/static-assets/ocr/content-code-examples/how-to/input-pdfs-read-pdf-pages.cs
using IronOcr;
using System.Collections.Generic;

// Instantiate IronTesseract
IronTesseract ocrTesseract = new IronTesseract();

// Create page indices list
List<int> pageIndices = new List<int>() { 0, 2 };

// Add PDF
using var pdfInput = new OcrPdfInput("Potter.pdf", PageIndices: pageIndices);
// Perform OCR
OcrResult ocrResult = ocrTesseract.Read(pdfInput);
Imports IronOcr
Imports System.Collections.Generic

' Instantiate IronTesseract
Private ocrTesseract As New IronTesseract()

' Create page indices list
Private pageIndices As New List(Of Integer)() From {0, 2}

' Add PDF
Private pdfInput = New OcrPdfInput("Potter.pdf", PageIndices:= pageIndices)
' Perform OCR
Private ocrResult As OcrResult = ocrTesseract.Read(pdfInput)
VB   C#

Specify Scan Region

By narrowing down the area to be read, you can significantly enhance the reading efficiency. To achieve this, you can specify the precise region of the imported PDF that needs to be read. In the code example below, I have instructed IronOcr to focus solely on extracting the chapter number and title.

:path=/static-assets/ocr/content-code-examples/how-to/input-pdfs-read-specific-region.cs
using IronOcr;
using IronSoftware.Drawing;

// Instantiate IronTesseract
IronTesseract ocrTesseract = new IronTesseract();

// Specify crop regions
CropRectangle[] scanRegions = { new CropRectangle(550, 100, 600, 300) };

// Add PDF
using (var pdfInput = new OcrPdfInput("Potter.pdf", ContentAreas: scanRegions))
{
    // Perform OCR
    OcrResult ocrResult = ocrTesseract.Read(pdfInput);

    // Output the result to console
    Console.WriteLine(ocrResult.Text);
}
Imports IronOcr
Imports IronSoftware.Drawing

' Instantiate IronTesseract
Private ocrTesseract As New IronTesseract()

' Specify crop regions
Private scanRegions() As CropRectangle = { New CropRectangle(550, 100, 600, 300) }

' Add PDF
Using pdfInput = New OcrPdfInput("Potter.pdf", ContentAreas:= scanRegions)
	' Perform OCR
	Dim ocrResult As OcrResult = ocrTesseract.Read(pdfInput)

	' Output the result to console
	Console.WriteLine(ocrResult.Text)
End Using
VB   C#

OCR Result

Read specific region

Chaknith Bin

Software Engineer

Chaknith is the Sherlock Holmes of developers. It first occurred to him he might have a future in software engineering, when he was doing code challenges for fun. His focus is on IronXL and IronBarcode, but he takes pride in helping customers with every product. Chaknith leverages his knowledge from talking directly with customers, to help further improve the products themselves. His anecdotal feedback goes beyond Jira tickets and supports product development, documentation and marketing, to improve customer’s overall experience.When he isn’t in the office, he can be found learning about machine learning, coding and hiking.