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Overview

The Syncfusion .NET PDF library makes it easy to merge or combine multiple PDF files into a single PDF document in C#. The process is simple and efficient, and the merged PDF files retain their original formatting, layout, annotations, bookmarks, form fields, and appearance.

The merge PDF feature works seamlessly on these platforms: WinForms, WPF, Blazor, .NET MAUI, .NET Core, WinUI, Xamarin, and UWP.

Merge PDF documentation

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.NET merge PDF

How to merge PDF files in C#

Install Syncfusion.Pdf.Net.Core NuGet package in your project.
Create a PdfDocument object.
Create two FileStream objects to represent the two input PDF files.
Call the PdfDocumentBase.Merge() method to merge the two input PDF files into the PdfDocument object.
Save the PdfDocument object to the MemoryStream object.

Here is an example of how to merge PDF files in C# using the Syncfusion .NET PDF library. You can merge multiple PDF files into a single PDF document with just a few lines of code.

c#
//Create a PDF document 
using (PdfDocument finalDocument = new PdfDocument()) 
{ 
    //Get the stream from an existing PDF document 
    using (FileStream firstStream = new FileStream("File1.pdf", FileMode.Open, FileAccess.Read)) 
    using (FileStream secondStream = new FileStream("File2.pdf", FileMode.Open, FileAccess.Read)) 
    { 
        //Create a PDF stream for merging 
        Stream[] streams = { firstStream, secondStream }; 
        //Merge PDF documents 
        PdfDocumentBase.Merge(finalDocument, streams); 
        //Save the document into a stream 
        using (MemoryStream outputStream = new MemoryStream()) 
        { 
            finalDocument.Save(outputStream); 
        } 
    } 
}

PDF - Merge options

Merge specific range of pages from different PDF documents

Merging specific ranges of pages from different PDF documents is a quick and easy way to combine different parts of documents into a single PDF document.

c#
//Create a new PDF document 
using (PdfDocument finalDocument = new PdfDocument()) 
{ 
    //Open the first PDF file
    using (FileStream firstStream = new FileStream("File1.pdf", FileMode.Open, FileAccess.Read)) 
    { 
        //Load the first PDF document 
        PdfLoadedDocument loadedDocument1 = new PdfLoadedDocument(firstStream); 
        //Import a range of pages from the first PDF document into the final document 
        //The range starts at page 2 and ends at the last page 
        finalDocument.ImportPageRange(loadedDocument1, 1, loadedDocument1.Pages.Count - 1); 
        //Open the second PDF file 
        using (FileStream secondStream = new FileStream("File2.pdf", FileMode.Open, FileAccess.Read)) 
        { 
            //Load the second PDF document 
            PdfLoadedDocument loadedDocument2 = new PdfLoadedDocument(secondStream);              
            //Import a range of pages from the second PDF document into the final document.
            //The range starts at page 2 and ends at page 5 
            finalDocument.ImportPageRange(loadedDocument2, 2, 5); 
            //Save the final document into a memory stream 
            using (MemoryStream outputStream = new MemoryStream()) 
            { 
                finalDocument.Save(outputStream); 
            } 
        } 
    } 
}

Extend margin

Extend the margin of PDF pages while merging PDF documents.

c#
//Create a new PDF document 
using (PdfDocument outputDocument = new PdfDocument()) 
{ 
    //Create a new instance for the document margin 
    PdfMargins documentMargins = new PdfMargins(); 
    //Set the margin to 50 points on all sides  
    documentMargins.All = 50; 
    //Set the document margins 
    outputDocument.PageSettings.Margins = documentMargins; 
    //Load the first PDF document 
    using (FileStream firstPDFStream = new FileStream("File1.pdf", FileMode.Open, FileAccess.Read)) 
    { 
        //Load the second PDF document 
        using (FileStream secondPDFStream = new FileStream("File2.pdf", FileMode.Open, FileAccess.Read)) 
        { 
            //Create a list of streams to merge 
            Stream[] streams = { firstPDFStream, secondPDFStream }; 
            //Create a merge options object 
            PdfMergeOptions mergeOptions = new PdfMergeOptions(); 
            //Enable the extend margin option 
            mergeOptions.ExtendMargin = true; 
            //Merge the PDF documents  
            PdfDocumentBase.Merge(outputDocument, mergeOptions, streams); 
            //Save the document to a memory stream 
            using (MemoryStream outputMemoryStream = new MemoryStream()) 
            { 
                outputDocument.Save(outputMemoryStream); 
            } 
        } 
    } 
}

Optimize PDF resources

Optimize PDF resources when merging multiple PDF documents into a single PDF document.

c#
//Create a new PDF document 
using (PdfDocument outputDocument = new PdfDocument()) 
{ 
    //Load the first PDF document
    using (FileStream firstPDFStream = new FileStream("File1.pdf", FileMode.Open, FileAccess.Read)) 
    { 
        //Load the second PDF document 
        using (FileStream secondPDFStream = new FileStream("File2.pdf", FileMode.Open, FileAccess.Read)) 
        { 
            //Create a list of streams to merge 
            Stream[] streams = { firstPDFStream, secondPDFStream }; 
            //Create a merge options object 
            PdfMergeOptions mergeOptions = new PdfMergeOptions(); 
            //Enable the optimize resources option 
            mergeOptions.OptimizeResources = true; 
            //Merge the PDF documents  
            PdfDocumentBase.Merge(outputDocument, mergeOptions, streams); 
            //Save the document to a memory stream 
            using (MemoryStream outputMemoryStream = new MemoryStream()) 
            { 
                outputDocument.Save(outputMemoryStream); 
            } 
        } 
    } 
}

Add bookmarks to merged PDF documents

When merging multiple PDF files, users can create bookmarks based on the titles of individual files. This will help quickly navigate to specific sections of the merged file.

c#
//Create a PDF document  
using (PdfDocument finalDocument = new PdfDocument()) 
{ 
    //Load the first PDF document 
    using (FileStream firstStream = new FileStream("File1.pdf", FileMode.Open, FileAccess.Read)) 
    //Load the second PDF document  
    using (FileStream secondStream = new FileStream("File2.pdf", FileMode.Open, FileAccess.Read)) 
    { 
        //Create a list of streams to merge   
        Stream[] streams = { firstStream, secondStream }; 
        //Merge PDF documents  
        PdfDocumentBase.Merge(finalDocument, streams); 
        //Create a bookmark for the first PDF file 
        PdfBookmark bookmark1 = finalDocument.Bookmarks.Add("Chapter 1 - Barcodes"); 
        //Set the destination page for the first bookmark  
        bookmark1.Destination = new PdfDestination(finalDocument.Pages[0]); 
        //Set the destination for the first bookmark  
        bookmark1.Destination.Location = new PointF(20, 20); 
        //Create a bookmark for the second PDF file 
        PdfBookmark bookmark2 = finalDocument.Bookmarks.Add("Chapter 2 - HTTP Succinctly"); 
        //Set the destination page for the second bookmark  
        bookmark2.Destination = new PdfDestination(finalDocument.Pages[3]); 
        //Set the destination  for the second bookmark 
        bookmark2.Destination.Location = new PointF(20, 20); 
        // Save the document into a stream  
        using (MemoryStream outputStream = new MemoryStream()) 
        { 
            finalDocument.Save(outputStream); 
        } 
    } 
}

Use cases

Merging PDF files using the Syncfusion.NET PDF library is a fast and efficient way to manage multiple PDF documents using C#. Besides this process, developers can also: