.NET PDF Merge Tasks with IronPDF: A Complete C# Guide

How Can You Merge PDF Documents Programmatically?

The PdfDocument.Merge method provides the simplest way to merge multiple PDF files into a single PDF. This merging PDF approach works seamlessly across .NET Framework, .NET Core, and .NET 8+ projects with no additional installation required beyond the NuGet package. The tool makes it extremely easy to create merged documents from separate files.

using IronPdf;
class Program
{
    static void Main(string[] args)
    {
        // Load two input PDF files from disk
        PdfDocument pdfA = PdfDocument.FromFile("invoice_one.pdf");
        PdfDocument pdfB = PdfDocument.FromFile("invoice_two.pdf");
        // Merge PDF documents into a single PDF
        PdfDocument merged = PdfDocument.Merge(pdfA, pdfB);
        // Save the merged document
        merged.SaveAs("combined_invoices.pdf");
    }
}

using IronPdf;
class Program
{
    static void Main(string[] args)
    {
        // Load two input PDF files from disk
        PdfDocument pdfA = PdfDocument.FromFile("invoice_one.pdf");
        PdfDocument pdfB = PdfDocument.FromFile("invoice_two.pdf");
        // Merge PDF documents into a single PDF
        PdfDocument merged = PdfDocument.Merge(pdfA, pdfB);
        // Save the merged document
        merged.SaveAs("combined_invoices.pdf");
    }
}

What Is the Best Way to Merge Multiple PDF Files?

When you need to merge multiple PDF documents beyond just two, IronPDF accepts a list of PDF files. This code sample shows how to combine multiple PDF files from different PDF documents into one consolidated file using the merging PDF tool:

using IronPdf;
using System.Collections.Generic;
class Program
{
    static void Main(string[] args)
    {
        // Create a list to hold existing PDF documents
        List<PdfDocument> pdfsToMerge = new List<PdfDocument>
        {
            PdfDocument.FromFile("report_q1.pdf"),
            PdfDocument.FromFile("report_q2.pdf"),
            PdfDocument.FromFile("report_q3.pdf"),
            PdfDocument.FromFile("report_q4.pdf")
        };
        // Merge multiple PDF files into a single PDF document
        PdfDocument merged = PdfDocument.Merge(pdfsToMerge);
        // Save the new PDF document
        merged.SaveAs("annual_report.pdf");
    }
}

using IronPdf;
using System.Collections.Generic;
class Program
{
    static void Main(string[] args)
    {
        // Create a list to hold existing PDF documents
        List<PdfDocument> pdfsToMerge = new List<PdfDocument>
        {
            PdfDocument.FromFile("report_q1.pdf"),
            PdfDocument.FromFile("report_q2.pdf"),
            PdfDocument.FromFile("report_q3.pdf"),
            PdfDocument.FromFile("report_q4.pdf")
        };
        // Merge multiple PDF files into a single PDF document
        PdfDocument merged = PdfDocument.Merge(pdfsToMerge);
        // Save the new PDF document
        merged.SaveAs("annual_report.pdf");
    }
}

How Can You Combine Existing PDF Documents with MemoryStream?

For scenarios requiring in-memory processing—such as a command line utility or web service—you can merge PDF files without writing documents to disk. Using a new MemoryStream approach, this merging PDF tool keeps everything in memory and can create output documents dynamically:

using IronPdf;
using System.IO;
class Program
{
    static void Main(string[] args)
    {
        // Load PDF files into memory streams
        byte[] firstFileBytes = File.ReadAllBytes("contract_part1.pdf");
        byte[] secondFileBytes = File.ReadAllBytes("contract_part2.pdf");
        // Create PDF documents from byte arrays
        PdfDocument doc1 = new PdfDocument(firstFileBytes);
        PdfDocument doc2 = new PdfDocument(secondFileBytes);
        // Merge and export to MemoryStream
        PdfDocument merged = PdfDocument.Merge(doc1, doc2);
        // Write to a new MemoryStream for further processing
        MemoryStream outputStream = merged.Stream;
        // Save the merged document
        merged.SaveAs("merged_contract.pdf");
    }
}

using IronPdf;
using System.IO;
class Program
{
    static void Main(string[] args)
    {
        // Load PDF files into memory streams
        byte[] firstFileBytes = File.ReadAllBytes("contract_part1.pdf");
        byte[] secondFileBytes = File.ReadAllBytes("contract_part2.pdf");
        // Create PDF documents from byte arrays
        PdfDocument doc1 = new PdfDocument(firstFileBytes);
        PdfDocument doc2 = new PdfDocument(secondFileBytes);
        // Merge and export to MemoryStream
        PdfDocument merged = PdfDocument.Merge(doc1, doc2);
        // Write to a new MemoryStream for further processing
        MemoryStream outputStream = merged.Stream;
        // Save the merged document
        merged.SaveAs("merged_contract.pdf");
    }
}

How Are Bookmarks and Security Handled in Merged PDF Files?

When you merge PDF files, IronPDF preserves file merge PDF bookmarks from the original documents. The merged document retains navigation elements across all pages, making it easy for readers to jump between sections from different PDF documents. All merged files maintain their bookmarks in the final output.

To password protect the resulted PDF document after merging:

// Apply security to the merged document
merged.SecuritySettings.UserPassword = "reader123";
merged.SecuritySettings.OwnerPassword = "admin456";
merged.SaveAs("secured_merged.pdf");

// Apply security to the merged document
merged.SecuritySettings.UserPassword = "reader123";
merged.SecuritySettings.OwnerPassword = "admin456";
merged.SaveAs("secured_merged.pdf");

You can also adjust the compression level to optimize file size, set the creation date metadata, or configure merged document rights to control what users can do with the output PDF file. These security features help create professional documents that meet your organization's requirements.

What Are Common Use Cases for PDF Merging?

PDF merge capabilities serve many practical scenarios in a .NET application when working with multiple PDF documents:

• Financial Reports: Combine existing PDF documents from quarterly statements into annual reports with merged pages
• Legal Documentation: Append contracts, amendments, and signatures into a single PDF file for archival
• Invoice Consolidation: Merge elements from multiple PDFs into one billing document with all pages combined
• Document Archival: Create consolidated records by merging PDF documents systematically across files

IronPDF also supports the ability to convert DOCX files to PDF before merging, allowing you to combine multiple PDFs that originated from different formats. The .NET assembly provides simple copy operations to extract specific pages before or after the merge process, giving you complete control over which documents and pages appear in your final merged output.

Conclusion: Streamlined PDF Merging in .NET

The examples throughout this article demonstrate just how easy and efficient it is to handle complex .NET PDF merge tasks within any C# or .NET application using IronPDF.

By utilizing the simple PdfDocument.Merge method, developers can quickly combine multiple PDF files, whether two separate documents, an entire list of files, or even documents loaded from MemoryStream, into a single, consolidated PDF.

• ✅ Simplicity: Minimal, clear C# code is required to achieve powerful results.
• ✅ Integrity: All original content, formatting, and bookmarks are preserved in the merged file.
• ✅ Flexibility: The approach works seamlessly across .NET Framework, .NET Core, and .NET 8+ projects.
• ✅ Functionality: Beyond merging, IronPDF offers robust features like password protection and further document manipulation, creating professional, secure, and well-organized output documents for diverse use cases—from financial reporting to legal archiving.

Ready to add PDF merge capabilities to your project? IronPDF makes merging PDF files in any .NET application straightforward with its intuitive API. The tool works across all major .NET platforms with the same simple syntax demonstrated in these code examples, handling documents and files of any complexity.

Get stated with IronPDF now.

Start for Free