Remove Attachment from PDF in C#

Introduction

Ever received a PDF loaded with unnecessary attachments that you need to strip out? Or maybe you’re building a document processing pipeline that requires cleaning up PDFs before archival? You’re in the right place.

Removing attachments from PDF documents programmatically is a common requirement in document management workflows—whether you’re sanitizing files for security compliance, reducing file sizes, or simply cleaning up before distribution. The challenge? Most PDF libraries make this task more complicated than it needs to be.

In this guide, you’ll learn how to remove attachments from PDF documents using C# and GroupDocs.Watermark for .NET. We’ll walk through a practical, production-ready approach that handles edge cases and gives you full control over which attachments to remove. By the end, you’ll have working code that you can drop straight into your project.

Why Remove PDF Attachments?

Before diving into the code, let’s talk about why you’d want to remove PDF attachments in the first place. Understanding the use cases helps you implement the right solution for your specific needs.

Common scenarios include:

  • Security and Compliance: Embedded files can contain malicious content or sensitive information. Many organizations strip attachments before sharing PDFs externally to minimize security risks.
  • File Size Optimization: Attachments significantly increase PDF file sizes. Removing unnecessary attachments can reduce storage costs and improve transfer speeds—especially important when dealing with thousands of documents.
  • Document Sanitization: When archiving or publishing documents, you might need to remove all embedded files to create clean, standalone PDFs that don’t rely on external content.
  • Automated Workflows: In document processing pipelines, removing specific types of attachments (like outdated templates or draft files) helps maintain consistency and quality control.

Pro tip: If you’re working with regulated industries (healthcare, finance, legal), attachment removal is often a required step in document preparation workflows to meet compliance standards.

Prerequisites

Before we dive into removing attachments from PDFs, make sure you have these basics covered:

1. Installation of GroupDocs.Watermark for .NET

You’ll need to download and install the GroupDocs.Watermark for .NET library. Grab it from the download page. The library supports .NET Framework 4.6.1+ and .NET Core 2.0+, so it’ll work with most modern .NET projects.

Installation via NuGet (recommended):

Install-Package GroupDocs.Watermark

This handles all dependencies automatically and keeps your project up-to-date with the latest version.

2. Basic Understanding of .NET Framework

You don’t need to be a .NET expert, but familiarity with basic concepts like namespaces, classes, and file I/O will help you understand what’s happening in the code. If you’re comfortable creating console applications or working with libraries in .NET, you’re good to go.

3. Familiarity with C# Programming Language

Since we’ll be working with C# code examples, you should know the fundamentals—variables, loops, conditional statements, and using statements. The code we’ll work with is straightforward, but understanding C# basics ensures you can adapt it to your specific requirements.

Quick check: If you’ve worked with file streams, LINQ, or third-party libraries in C# before, you’ll find this tutorial easy to follow.

Import Namespaces

To start working with GroupDocs.Watermark for .NET, you need to import the necessary namespaces into your project. This gives you access to all the classes and methods we’ll use to manipulate PDF attachments.

Add these using statements at the top of your C# file:

using GroupDocs.Watermark.Common;
using GroupDocs.Watermark.Contents.Pdf;
using GroupDocs.Watermark.Options.Pdf;
using System.IO;
using System;

What each namespace does:

  • GroupDocs.Watermark.Common: Core classes and enumerations used throughout the library
  • GroupDocs.Watermark.Contents.Pdf: PDF-specific content handling, including attachment management
  • GroupDocs.Watermark.Options.Pdf: Configuration options for loading and saving PDF documents
  • System.IO: Standard .NET file operations (we’ll use this for path handling)
  • System: Basic system functionality (used for exception handling and console output)

These namespaces form the foundation of our attachment removal functionality, giving you everything needed to load PDFs, inspect attachments, and save modified documents.

Step-by-Step Guide: Remove Attachments from PDF

Now let’s get into the actual process of removing attachments from PDF documents using GroupDocs.Watermark for .NET. We’ll break this down into clear, manageable steps that you can follow along with.

Step 1: Define Document Path and Output Directory

string documentPath = "Your Document Path";
string outputDirectory = "Your Document Directory";
string outputFileName = Path.Combine(outputDirectory, Path.GetFileName(documentPath));

First things first—you need to tell the program where to find your PDF and where to save the modified version.

Here’s what’s happening:

  • documentPath: The full path to your source PDF file (the one with attachments you want to remove)
  • outputDirectory: Where you want to save the cleaned-up PDF
  • outputFileName: Combines the output directory with the original filename, so your modified file has the same name but lives in a different location

Real-world tip: In production environments, you’ll typically pull these paths from configuration files, environment variables, or user input. For testing, you can hardcode them like: string documentPath = @"C:\Documents\sample-with-attachments.pdf";

Step 2: Load PDF Document with Options

var loadOptions = new PdfLoadOptions();

Here we’re creating a PdfLoadOptions object, which lets you customize how the PDF is loaded. While we’re using the default options in this example, this object is your gateway to advanced configurations.

What you can do with load options:

  • Set password protection handling for encrypted PDFs
  • Configure memory usage optimization for large files
  • Specify encoding options for special character handling
  • Enable or disable certain PDF features during loading

For most scenarios (including this one), the default settings work perfectly. But if you’re dealing with password-protected PDFs or need performance tuning for massive files, this is where you’d add those configurations.

Step 3: Initialize Watermarker

using (Watermarker watermarker = new Watermarker(documentPath, loadOptions))

Now we’re creating a Watermarker object—this is your primary tool for working with the PDF. The using statement is crucial here because it ensures the document is properly closed and resources are released when we’re done.

Why this matters:

  • The Watermarker loads the entire PDF into memory and locks the file
  • Without proper disposal (which using handles automatically), you could end up with locked files or memory leaks
  • This object gives you access to everything inside the PDF—attachments, watermarks, annotations, and more

Think of the Watermarker as your “document session.” Everything you do to the PDF happens through this object, and when the using block ends, all changes are finalized and the file is released.

Step 4: Get PDF Content

PdfContent pdfContent = watermarker.GetContent<PdfContent>();

This line retrieves the actual content structure of your PDF document. The GetContent<PdfContent>() method returns a strongly-typed object that represents all the PDF’s internal components.

What you gain access to:

  • Attachments collection (what we’re after)
  • Pages and their content
  • Watermarks and annotations
  • Document metadata and properties
  • Form fields and interactive elements

Using the generic GetContent<T>() approach ensures type safety and gives you IntelliSense support in Visual Studio, making it easier to explore what you can do with the PDF. For other document types (Word, Excel, etc.), you’d use different type parameters like WordProcessingContent or SpreadsheetContent.

Step 5: Iterate Through Attachments and Remove

for (int i = pdfContent.Attachments.Count - 1; i >= 0; i--)
{
    PdfAttachment attachment = pdfContent.Attachments[i];
    if (attachment.Name.Contains("sample") && attachment.GetDocumentInfo().FileType == FileType.DOCX)
    {
        pdfContent.Attachments.RemoveAt(i);
    }
}

This is where the magic happens. We’re looping through all attachments in the PDF and removing the ones that match our criteria.

Key things to notice:

1. We iterate backwards (i-- starting from Count - 1): This is a critical best practice when removing items from a collection while looping. If you iterate forward and remove items, you’ll skip elements because the indices shift after each removal. Backward iteration avoids this problem entirely.

2. Conditional removal: In this example, we’re removing attachments where:

  • The attachment name contains “sample” (case-sensitive)
  • The file type is DOCX (Microsoft Word document)

Customize the condition for your needs:

// Remove ALL attachments
pdfContent.Attachments.RemoveAt(i);

// Remove by file extension
if (attachment.Name.EndsWith(".exe") || attachment.Name.EndsWith(".zip"))

// Remove by size (attachments larger than 5MB)
if (attachment.Content.Length > 5 * 1024 * 1024)

// Remove by creation date (older than 1 year)
if (attachment.GetDocumentInfo().CreationDate < DateTime.Now.AddYears(-1))

Available attachment properties:

  • Name: Filename of the attachment
  • Description: Optional description metadata
  • Content: Raw byte array of the file
  • GetDocumentInfo(): Returns file type, creation date, and other metadata

This flexibility lets you implement sophisticated filtering logic based on your specific document management requirements.

Step 6: Save Modified Document

watermarker.Save(outputFileName);

The final step—saving your cleaned-up PDF to the specified output location. This method writes all changes to disk and creates your new PDF file without the removed attachments.

What happens during save:

  • All modifications (removed attachments) are committed to the document structure
  • The PDF is rewritten to the output path you specified in Step 1
  • Original PDF remains unchanged (we’re saving to a new file)
  • Document structure and integrity are preserved

Important considerations:

  • Make sure the output directory exists before saving, or you’ll get an exception
  • If a file with the same name exists at the output path, it will be overwritten
  • The save operation can take a few seconds for large PDFs (hundreds of pages)

Error handling best practice:

try
{
    watermarker.Save(outputFileName);
    Console.WriteLine($"Successfully saved cleaned PDF to: {outputFileName}");
}
catch (Exception ex)
{
    Console.WriteLine($"Error saving file: {ex.Message}");
}

After this step completes, you’ll have a new PDF file that’s identical to the original except for the attachments you removed. The file is ready to use, share, or process further in your workflow.

Common Use Cases

Understanding when and how to remove PDF attachments helps you apply this technique effectively in real-world scenarios. Here are some practical situations where attachment removal becomes essential:

1. Document Archival and Compliance

Organizations often need to archive PDFs in a standardized format without embedded files. Legal departments, healthcare providers, and financial institutions frequently strip attachments before long-term storage to:

  • Ensure documents can be opened years later without dependency issues
  • Meet regulatory requirements that specify plain PDF formats
  • Reduce storage costs in document management systems
  • Simplify e-discovery and document retrieval processes

2. Email and File Sharing Workflows

Before distributing PDFs externally, you might need to remove attachments to:

  • Reduce email attachment sizes and avoid bounce-backs
  • Strip internal documentation that shouldn’t be shared with clients
  • Remove draft versions or working files embedded during document creation
  • Ensure recipients only see finalized, published content

3. Security and Malware Prevention

Attachments can pose security risks, especially in automated workflows:

  • Remove executable files (.exe, .bat) that could contain malware
  • Strip potentially dangerous file types before routing documents through systems
  • Sanitize PDFs from untrusted sources before opening them in your environment
  • Clean up files before importing into secure document repositories

4. Batch Document Processing

In automated document pipelines, you might:

  • Remove all attachments from thousands of PDFs as part of a migration project
  • Clean up vendor-supplied documents that include unnecessary supplementary files
  • Standardize document formats across your organization
  • Prepare documents for conversion to other formats (where attachments might not be supported)

Troubleshooting Common Issues

When working with PDF attachment removal, you might encounter a few common challenges. Here’s how to address them:

Issue 1: “File is being used by another process”

Symptom: Exception thrown when trying to save the modified PDF.

Solution: Make sure you’re using the using statement with the Watermarker object (as shown in Step 3). This ensures the file handle is properly released. If you’re still having issues, check that no other application (like Adobe Reader) has the PDF open.

// Good - automatic disposal
using (Watermarker watermarker = new Watermarker(documentPath, loadOptions))
{
    // Your code here
} // File handle released here

// Bad - might leave file locked
Watermarker watermarker = new Watermarker(documentPath, loadOptions);
// If exception occurs before disposal, file stays locked

Issue 2: Password-Protected PDFs

Symptom: Exception when trying to load a password-protected PDF.

Solution: Add the password to your load options:

var loadOptions = new PdfLoadOptions 
{ 
    Password = "your-pdf-password" 
};

If you’re processing multiple PDFs with different passwords, you’ll need to handle password management in your application logic.

Issue 3: Attachment Not Found by Name

Symptom: Your conditional check doesn’t find the attachments you’re looking for.

Solution: Attachment names can be case-sensitive and might include file extensions. Try more flexible matching:

// Case-insensitive search
if (attachment.Name.ToLower().Contains("sample"))

// Check without extension
string nameWithoutExt = Path.GetFileNameWithoutExtension(attachment.Name);
if (nameWithoutExt.Equals("document", StringComparison.OrdinalIgnoreCase))

Issue 4: Large PDF Performance Issues

Symptom: Processing very large PDFs (50+ MB) takes too long or causes memory issues.

Solution: Consider processing PDFs in batches or implementing streaming approaches for extremely large files. You can also:

  • Increase application memory allocation if running in constrained environments
  • Process PDFs asynchronously to avoid blocking your main application thread
  • Implement progress reporting for long-running operations

Issue 5: Corrupted PDF After Saving

Symptom: The saved PDF won’t open or displays errors.

Solution: This is rare but can happen with malformed source PDFs. Always:

  • Validate that your source PDF opens correctly before processing
  • Implement try-catch blocks around the save operation
  • Keep backups of original files until you’ve verified the output
  • Test with a small sample of PDFs before batch processing thousands

Best Practices

Follow these guidelines to implement robust, production-ready PDF attachment removal:

Performance Optimization

1. Batch Processing: If you’re removing attachments from multiple PDFs, reuse the same logic in a loop but create new Watermarker instances for each file:

foreach (string pdfPath in Directory.GetFiles(@"C:\PDFs", "*.pdf"))
{
    using (Watermarker watermarker = new Watermarker(pdfPath, loadOptions))
    {
        // Process each PDF
    }
}

2. Selective Loading: If you only need to work with attachments, you can optimize memory usage by not loading unnecessary PDF elements. While GroupDocs.Watermark handles this automatically, be mindful of processing very large PDFs with many pages.

3. Parallel Processing: For large batches, consider using parallel processing with Parallel.ForEach(), but be careful with resource limits:

Parallel.ForEach(pdfFiles, new ParallelOptions { MaxDegreeOfParallelism = 4 }, pdfPath => 
{
    // Process each PDF in parallel
});

Security Considerations

1. Validate File Types: Before processing, verify you’re actually working with PDF files:

if (Path.GetExtension(documentPath).ToLower() != ".pdf")
{
    throw new ArgumentException("Only PDF files are supported");
}

2. Sanitize File Paths: When accepting user input for file paths, validate and sanitize to prevent path traversal attacks.

3. Audit Trail: Log which attachments were removed and when, especially in compliance-sensitive environments:

foreach (var attachment in attachments)
{
    Console.WriteLine($"Removed attachment: {attachment.Name} at {DateTime.Now}");
}

Code Maintainability

1. Extract Logic: If you’re using complex removal conditions, extract them into separate methods:

private bool ShouldRemoveAttachment(PdfAttachment attachment)
{
    return attachment.Name.Contains("draft") || 
           attachment.GetDocumentInfo().FileType == FileType.EXE ||
           attachment.Content.Length > 10 * 1024 * 1024;
}

2. Configuration Over Code: Store removal criteria in configuration files rather than hardcoding them:

// Read from appsettings.json
var excludedExtensions = configuration.GetSection("AttachmentFilters:ExcludedExtensions").Get<List<string>>();

3. Error Handling: Implement comprehensive error handling that doesn’t stop processing if one PDF fails:

foreach (var pdfPath in pdfFiles)
{
    try
    {
        // Process PDF
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Failed to process {pdfPath}: {ex.Message}");
        // Log and continue with next file
    }
}

Conclusion

Removing attachments from PDF documents using GroupDocs.Watermark for .NET is straightforward once you understand the workflow. By following the step-by-step approach in this guide, you can efficiently clean up PDFs—whether you’re processing a single file or implementing an automated document management pipeline.

Key takeaways:

  • Always iterate backwards when removing items from collections to avoid index shifting issues
  • Use the using statement with Watermarker to ensure proper resource disposal
  • Customize removal conditions based on attachment names, file types, sizes, or other properties
  • Implement error handling and logging for production environments
  • Consider performance optimization when batch processing large numbers of PDFs

The code examples provided are production-ready and can be adapted to your specific requirements. Whether you’re building a document sanitization tool, implementing security compliance workflows, or simply need to manage PDF attachments programmatically, GroupDocs.Watermark for .NET gives you the flexibility and control you need.

Ready to take it further? Explore the GroupDocs.Watermark documentation for advanced features like adding watermarks, extracting text, and working with other document formats beyond PDFs.

FAQ’s

Is GroupDocs.Watermark for .NET compatible with other document formats besides PDF?

Yes! GroupDocs.Watermark for .NET supports a wide range of document formats including Word (DOC, DOCX), Excel (XLS, XLSX), PowerPoint (PPT, PPTX), images (PNG, JPG), and more. You can use similar techniques to manage watermarks and attachments across different file types in your .NET applications.

Can I add custom watermarks to PDF documents using GroupDocs.Watermark for .NET?

Absolutely. GroupDocs.Watermark for .NET specializes in watermark manipulation—you can add text watermarks, image watermarks, or even complex multi-layer watermarks to PDFs. You have full control over positioning, opacity, rotation, and styling. Check the documentation for watermark-specific examples.

Does GroupDocs.Watermark for .NET offer cross-platform compatibility?

Yes, GroupDocs.Watermark for .NET works seamlessly across Windows, Linux, and macOS. It supports both .NET Framework (4.6.1+) and .NET Core (2.0+), so you can run your PDF processing code on any platform that supports .NET. This makes it ideal for cloud-based or containerized applications.

Is there a trial version available for GroupDocs.Watermark for .NET?

Yes, you can access a free trial version to test the library’s capabilities before purchasing. Visit the GroupDocs releases page to download the trial. The trial version lets you evaluate all features, though it may include evaluation watermarks on output documents.

How can I get technical assistance or support for GroupDocs.Watermark for .NET?

For technical help, bug reports, or feature discussions, visit the GroupDocs.Watermark forum. The community and GroupDocs support team actively respond to questions. You can also access comprehensive documentation, code examples, and API references on the official documentation site.

Can I remove all attachments from a PDF at once?

Yes! Simply remove the condition from the loop in Step 5. Instead of checking attachment names or file types, just call pdfContent.Attachments.RemoveAt(i) for every attachment. This removes all embedded files in one pass through the attachments collection.

What’s the maximum PDF file size GroupDocs.Watermark can handle?

GroupDocs.Watermark for .NET can handle large PDFs (hundreds of megabytes), but performance depends on your system’s available memory and resources. For extremely large files (1GB+), consider implementing streaming approaches or processing on a server with adequate RAM. Most typical business PDFs (under 50MB) process quickly without special optimization.

Does removing attachments affect the PDF’s visual appearance or content?

No. Removing attachments only eliminates the embedded files—it doesn’t change the visual content, text, images, or layout of the PDF pages themselves. The document looks identical; it just no longer contains the attached files that were embedded within it. This is perfect for situations where you need to preserve the document’s appearance while cleaning up additional embedded content.