Scanned PDF to Text
How to Extract Text from Scanned PDFs with Aspose.OCR

How to Extract Text from Scanned PDFs with Aspose.OCR

Extracting text from scanned or image-based PDF files used to require complex workflows or expensive manual labor. With Aspose.OCR Scanned PDF to Text for .NET, you can automate this process, converting PDFs to searchable and editable text with just a few lines of code.

Real-World Problem

Organizations often receive contracts, reports, or archives as scanned PDFs. Manually copying text or searching inside these documents is tedious and error-prone, slowing down compliance, archiving, and digital transformation projects.

Solution Overview

Aspose.OCR for .NET lets you batch process scanned PDFs—turning them into text or searchable PDFs, making information accessible, indexable, and ready for digital workflows. It’s fast, accurate, and requires minimal code.

Prerequisites

Before you start, ensure you have:

  1. Visual Studio 2019 or later
  2. .NET 6.0 or later (or .NET Framework 4.6.2+)
  3. Aspose.OCR for .NET from NuGet
  4. Basic C# knowledge
PM> Install-Package Aspose.OCR

Step-by-Step Implementation

Step 1: Install and Configure Aspose.OCR

Add the NuGet package and reference Aspose.OCR:

using Aspose.OCR;

Step 2: Add Your Scanned PDF Files

Create an OcrInput object for PDF input and add your scanned PDF files.

OcrInput input = new OcrInput(InputType.PDF);
input.Add("contract.pdf");
input.Add("archive.pdf");
// Optionally specify page ranges:
// input.Add("report.pdf", startPage: 0, pagesCount: 5);

Step 3: Configure Recognition Settings

Configure language and other recognition settings to suit your documents.

RecognitionSettings settings = new RecognitionSettings();
settings.Language = Language.English;

Step 4: Run the Recognition Process

Recognize text from your scanned PDFs:

AsposeOcr ocr = new AsposeOcr();
List<RecognitionResult> results = ocr.Recognize(input, settings);

Step 5: Save or Export Recognized Text

Export the recognized text to files, or convert the results to searchable PDFs.

foreach (RecognitionResult result in results)
{
    Console.WriteLine(result.RecognitionText); // Show the text in console
    result.Save("output.txt", SaveFormat.Text); // Save as plain text
    result.Save("output.pdf", SaveFormat.Pdf); // Save as searchable PDF
}

Step 6: Add Error Handling

Wrap recognition in a try/catch block for robustness.

try
{
    AsposeOcr ocr = new AsposeOcr();
    List<RecognitionResult> results = ocr.Recognize(input, settings);
    // Further processing...
}
catch (Exception ex)
{
    Console.WriteLine($"Error: {ex.Message}");
}

Step 7: Optimize for Large or Multi-page PDFs

  • Process PDFs page by page for huge files
  • Use high-quality scans for best results
  • Batch process in parallel for large collections
// Example: Add all scanned PDFs in a folder
foreach (string file in Directory.GetFiles("./pdfs", "*.pdf"))
{
    input.Add(file);
}

Step 8: Complete Working Example 

using Aspose.OCR;
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        try
        {
            OcrInput input = new OcrInput(InputType.PDF);
            input.Add("contract.pdf");
            input.Add("archive.pdf");

            RecognitionSettings settings = new RecognitionSettings();
            settings.Language = Language.English;

            AsposeOcr ocr = new AsposeOcr();
            List<RecognitionResult> results = ocr.Recognize(input, settings);

            foreach (RecognitionResult result in results)
            {
                Console.WriteLine(result.RecognitionText);
                result.Save("output.txt", SaveFormat.Text);
                result.Save("output.pdf", SaveFormat.Pdf);
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
        }
    }
}

Use Cases and Applications

Digital Archiving

Convert entire libraries of scanned documents into searchable, indexable files for compliance and knowledge management.

Legal and Contract Management

Extract contract clauses or terms from PDFs for review, automation, or digital signing.

Streamlined Document Search

Enable fast full-text search in archives, knowledge bases, or case files.

Common Challenges and Solutions

Challenge 1: Low-Quality or Skewed Scans

Solution: Use pre-processing filters and high-quality scans where possible.

Challenge 2: Multi-language PDFs

Solution: Set the language in recognition settings or process with multiple language options.

Challenge 3: Very Large PDF Files

Solution: Process in batches or per page, and monitor memory usage.

Performance Considerations

  • Use optimal DPI (300+) for scanned PDFs
  • Batch process for best throughput
  • Dispose OCR objects and close file handles

Best Practices

  1. Validate OCR output before further automation
  2. Organize and backup original PDF files
  3. Use the correct SaveFormat for your workflow
  4. Regularly update Aspose.OCR for new PDF features

Advanced Scenarios

Scenario 1: Extract Only Specific Pages from a PDF 

input.Add("archive.pdf", startPage: 5, pagesCount: 3);

Scenario 2: Exporting to Multiple Formats 

foreach (RecognitionResult result in results)
{
    result.Save("output.docx", SaveFormat.Docx);
    result.Save("output.json", SaveFormat.Json);
}

Conclusion

Aspose.OCR for .NET lets you convert scanned PDFs to actionable text and searchable files—eliminating manual entry and making information accessible to your entire organization.

For more details and examples, see the Aspose.OCR for .NET API Reference .

 English