Flatten PDFs in C#

How Can I Verify the PDF Is Flattened?

The output below shows the before and after states. The first PDF contains editable form fields. After applying IronPDF's flatten method, the document becomes completely non-editable. This code works in any .NET project, including ASP.NET applications and Blazor servers.

To verify successful flattening, check the form field count:

using IronPdf;

// Load the flattened PDF
PdfDocument flattenedPdf = PdfDocument.FromFile("flattened.pdf");

// Check if any form fields exist
if (flattenedPdf.Form.Fields.Count == 0)
{
    Console.WriteLine("PDF has been successfully flattened - no interactive fields remain.");
}
else
{
    Console.WriteLine($"Warning: {flattenedPdf.Form.Fields.Count} form fields still exist.");
}

using IronPdf;

// Load the flattened PDF
PdfDocument flattenedPdf = PdfDocument.FromFile("flattened.pdf");

// Check if any form fields exist
if (flattenedPdf.Form.Fields.Count == 0)
{
    Console.WriteLine("PDF has been successfully flattened - no interactive fields remain.");
}
else
{
    Console.WriteLine($"Warning: {flattenedPdf.Form.Fields.Count} form fields still exist.");
}

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What Happens to Form Fields After Flattening?

When you flatten a PDF document, all interactive form elements undergo permanent transformation. Form fields convert into static page content, becoming part of the document's visual layer:

• Text fields become regular text on the page
• Checkboxes and radio buttons become static images showing their selected state
• Dropdown menus display only the selected value as plain text
• Digital signatures are preserved visually but lose cryptographic validation

This process is irreversible. Keep a copy of the original interactive PDF if you need future editing capabilities. For documents requiring both security and editability, use PDF permissions and passwords instead of flattening.

When Should I Flatten My PDF Documents?

PDF flattening is essential in these business scenarios:

1. Legal Document Archival: Flatten contracts and agreements after signing to prevent content alteration and maintain legal integrity.

2. Report Distribution: Flatten financial reports and data sheets with calculated fields before distribution to prevent tampering.

3. Form Submission Processing: Create permanent records by flattening PDFs after users complete online forms.

4. Printing Optimization: Flattened PDFs print more reliably since printers don't process interactive elements.

5. File Size Reduction: Flattening can reduce file size by removing form field data structures when using PDF compression.

Here's a batch processing example for archiving multiple completed forms:

using IronPdf;
using System.IO;

public class BatchPdfFlattener
{
    public static void FlattenAllPdfsInDirectory(string sourceDir, string outputDir)
    {
        // Ensure output directory exists
        Directory.CreateDirectory(outputDir);

        // Get all PDF files in source directory
        string[] pdfFiles = Directory.GetFiles(sourceDir, "*.pdf");

        foreach (string pdfFile in pdfFiles)
        {
            try
            {
                // Load the PDF
                PdfDocument pdf = PdfDocument.FromFile(pdfFile);

                // Flatten the document
                pdf.Flatten();

                // Save to output directory with "_flattened" suffix
                string fileName = Path.GetFileNameWithoutExtension(pdfFile);
                string outputPath = Path.Combine(outputDir, $"{fileName}_flattened.pdf");
                pdf.SaveAs(outputPath);

                Console.WriteLine($"Flattened: {fileName}");
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error processing {pdfFile}: {ex.Message}");
            }
        }
    }
}

using IronPdf;
using System.IO;

public class BatchPdfFlattener
{
    public static void FlattenAllPdfsInDirectory(string sourceDir, string outputDir)
    {
        // Ensure output directory exists
        Directory.CreateDirectory(outputDir);

        // Get all PDF files in source directory
        string[] pdfFiles = Directory.GetFiles(sourceDir, "*.pdf");

        foreach (string pdfFile in pdfFiles)
        {
            try
            {
                // Load the PDF
                PdfDocument pdf = PdfDocument.FromFile(pdfFile);

                // Flatten the document
                pdf.Flatten();

                // Save to output directory with "_flattened" suffix
                string fileName = Path.GetFileNameWithoutExtension(pdfFile);
                string outputPath = Path.Combine(outputDir, $"{fileName}_flattened.pdf");
                pdf.SaveAs(outputPath);

                Console.WriteLine($"Flattened: {fileName}");
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error processing {pdfFile}: {ex.Message}");
            }
        }
    }
}

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For advanced PDF manipulation techniques, including merging or splitting PDFs after flattening, see IronPDF's comprehensive documentation.

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Read More Documentation

Read the Documentation for more on how to flatten PDFs, edit and manipulate them, and more.

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Ready to see what else you can do? Check out our tutorial page here: Additional Features