Java Merge PDF Files into a Single PDF

IronPDF: Java Library

IronPDF is a Java library for creating, reading, and editing single or multiple PDF documents. It allows its users to create all the PDF files from scratch, including the content appearance using HTML rendering, as well as metadata such as title and author name. The library also allows merging multiple PDF files, making it easy to combine the content into one PDF destination file path. It does not require any third-party libraries, external frameworks, or platform integration for working with PDF files or PDF iterator objects. It also provides Cross Platform Support. It is designed specifically for Java 8+, Kotlin, and Scala running on Windows, Linux, and Cloud platforms.

Prerequisites

To merge multiple PDF files, you will need the following:

1. Any Java-supported IDE (Netbeans, Eclipse, IntelliJ, etc). We will be using IntelliJ here to merge multiple PDFs.
2. A Maven project running in the IDE.

Install IronPDF

The first thing we need, to merge PDF files, is the IronPDF Java library. There are three ways to download and install IronPDF in any project.

1. You can add the IronPDF dependency in the pom.xml file of a Maven project and use the Maven command-line tool or an IDE to download the library directly from the central repository.
2. Another way is to visit the Maven website and download the latest version of IronPDF. You can download it from here directly.
3. You can also visit the IronPDF website to download directly through this link.

In each case, the following dependency code is added to the pom.xml file.

<dependency>
    <groupId>com.ironsoftware</groupId>
    <artifactId>ironpdf</artifactId>
    <version>YOUR_VERSION_HERE</version>
</dependency>

<dependency>
    <groupId>com.ironsoftware</groupId>
    <artifactId>ironpdf</artifactId>
    <version>YOUR_VERSION_HERE</version>
</dependency>

One more dependency required to merge PDFs is Slf4j-simple. You can also add it to the pom.xml file using the following code or you can visit the Maven website here.

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-simple</artifactId>
    <version>2.0.5</version>
</dependency>

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-simple</artifactId>
    <version>2.0.5</version>
</dependency>

pom.xml dependencies

The following import statements are also required in the main.java file, to use IronPDF functions for merging PDF files.

import com.ironsoftware.ironpdf.PdfDocument;
import java.io.IOException;
import java.nio.file.Paths;

import com.ironsoftware.ironpdf.PdfDocument;
import java.io.IOException;
import java.nio.file.Paths;

Merge Two PDF Source Files in Java using IronPDF

To merge PDF files, first we need to create PDF files and then convert them to a final merged PDF file. The following code sample will do just that:

String htmlA = "<p> [PDF_A] </p>"
        + "<p> [PDF_A] 1st Page </p>"
        + "<div style='page-break-after: always;'></div>"
        + "<p> [PDF_A] 2nd Page</p>";
String htmlB = "<p> [PDF_B] </p>"
        + "<p> [PDF_B] 1st Page </p>"
        + "<div style='page-break-after: always;'></div>"
        + "<p> [PDF_B] 2nd Page</p>";

// Create PdfDocument objects using the HTML content
PdfDocument pdfA = PdfDocument.renderHtmlAsPdf(htmlA);
PdfDocument pdfB = PdfDocument.renderHtmlAsPdf(htmlB);

// Merge the two PDF documents into a single document
PdfDocument merged = PdfDocument.merge(pdfA, pdfB);

String htmlA = "<p> [PDF_A] </p>"
        + "<p> [PDF_A] 1st Page </p>"
        + "<div style='page-break-after: always;'></div>"
        + "<p> [PDF_A] 2nd Page</p>";
String htmlB = "<p> [PDF_B] </p>"
        + "<p> [PDF_B] 1st Page </p>"
        + "<div style='page-break-after: always;'></div>"
        + "<p> [PDF_B] 2nd Page</p>";

// Create PdfDocument objects using the HTML content
PdfDocument pdfA = PdfDocument.renderHtmlAsPdf(htmlA);
PdfDocument pdfB = PdfDocument.renderHtmlAsPdf(htmlB);

// Merge the two PDF documents into a single document
PdfDocument merged = PdfDocument.merge(pdfA, pdfB);

The above code creates two strings containing HTML markup. The HTML content for each variable spans two pages. Then, IronPDF's renderHtmlAsPdf method is called to convert both HTML strings into individual PDF documents.

The method to merge PDF files together is PdfDocument.merge. This method is called above to merge the two PDF documents into a single one. The result is a new PdfDocument produced by appending the content of the second PdfDocument to the end of the first one.

Save Merged Multiple PDF Document

To save the merged PDF file to your desired destination file path, simply use the following line:

merged.saveAs(Paths.get("assets/merged.pdf"));

merged.saveAs(Paths.get("assets/merged.pdf"));

JAVA

The output of the merged PDF file is shown below:

Merge Multiple PDF Documents

Merge More Than Two PDF Files

To merge more than two PDF documents, first we will create a collection containing the required PdfDocument objects, and then pass the list as a single argument to the PdfDocument.merge method. The code goes as follows:

import java.util.List;
import java.util.ArrayList;

public static void main(String[] args) throws IOException {
    String htmlA = "<p> [PDF_A] </p>"
            + "<p> [PDF_A] 1st Page </p>"
            + "<div style='page-break-after: always;'></div>"
            + "<p> [PDF_A] 2nd Page</p>";
    String htmlB = "<p> [PDF_B] </p>"
            + "<p> [PDF_B] 1st Page </p>"
            + "<div style='page-break-after: always;'></div>"
            + "<p> [PDF_B] 2nd Page</p>";
    String htmlC = "<p> [PDF_C] </p>"
            + "<p> [PDF_C] 1st Page </p>"
            + "<div style='page-break-after: always;'></div>"
            + "<p> [PDF_C] 2nd Page</p>";
    String htmlD = "<p> [PDF_D] </p>"
            + "<p> [PDF_D] 1st Page </p>"
            + "<div style='page-break-after: always;'></div>"
            + "<p> [PDF_D] 2nd Page</p>";

    // Creating PdfDocument objects
    PdfDocument pdfA = PdfDocument.renderHtmlAsPdf(htmlA);
    PdfDocument pdfB = PdfDocument.renderHtmlAsPdf(htmlB);
    PdfDocument pdfC = PdfDocument.renderHtmlAsPdf(htmlC);
    PdfDocument pdfD = PdfDocument.renderHtmlAsPdf(htmlD);

    // Add documents to a list
    List<PdfDocument> pdfs = new ArrayList<>();
    pdfs.add(pdfA);
    pdfs.add(pdfB);
    pdfs.add(pdfC);
    pdfs.add(pdfD);

    // Merge all documents into a single PDF
    PdfDocument merged = PdfDocument.merge(pdfs);

    // Save the merged PDF document
    merged.saveAs(Paths.get("assets/more_than_two_merged.pdf"));
}

import java.util.List;
import java.util.ArrayList;

public static void main(String[] args) throws IOException {
    String htmlA = "<p> [PDF_A] </p>"
            + "<p> [PDF_A] 1st Page </p>"
            + "<div style='page-break-after: always;'></div>"
            + "<p> [PDF_A] 2nd Page</p>";
    String htmlB = "<p> [PDF_B] </p>"
            + "<p> [PDF_B] 1st Page </p>"
            + "<div style='page-break-after: always;'></div>"
            + "<p> [PDF_B] 2nd Page</p>";
    String htmlC = "<p> [PDF_C] </p>"
            + "<p> [PDF_C] 1st Page </p>"
            + "<div style='page-break-after: always;'></div>"
            + "<p> [PDF_C] 2nd Page</p>";
    String htmlD = "<p> [PDF_D] </p>"
            + "<p> [PDF_D] 1st Page </p>"
            + "<div style='page-break-after: always;'></div>"
            + "<p> [PDF_D] 2nd Page</p>";

    // Creating PdfDocument objects
    PdfDocument pdfA = PdfDocument.renderHtmlAsPdf(htmlA);
    PdfDocument pdfB = PdfDocument.renderHtmlAsPdf(htmlB);
    PdfDocument pdfC = PdfDocument.renderHtmlAsPdf(htmlC);
    PdfDocument pdfD = PdfDocument.renderHtmlAsPdf(htmlD);

    // Add documents to a list
    List<PdfDocument> pdfs = new ArrayList<>();
    pdfs.add(pdfA);
    pdfs.add(pdfB);
    pdfs.add(pdfC);
    pdfs.add(pdfD);

    // Merge all documents into a single PDF
    PdfDocument merged = PdfDocument.merge(pdfs);

    // Save the merged PDF document
    merged.saveAs(Paths.get("assets/more_than_two_merged.pdf"));
}

JAVA

Four PDF documents are created above using the HTML render method. Next, we populate a new List collection with each of the PDFs, and then pass this list to the merge method as a single argument. As a result, these PDFs are merged into a single PDF document.

More Than Two Merged PDF Files

Conclusion

This article explained how to merge PDF files together using IronPDF for Java.

We first covered how to install IronPDF for Java using Maven, and then we showed a simple way to produce PDFs using the HTML rendering methods. Afterward, we saw how to merge two or more PDFs into a single PDF file.

IronPDF performs very well and carries out all operations with speed and accuracy. It is an excellent option for working with PDF files in Java. Moreover, it is based on IronPDF for .NET capabilities.

The IronEngine for Java allows HTML/URL/String to PDF conversion with open standard document types such as HTML, CSS, JS, JPG, and PNG. It produces pixel-perfect PDF documents and is built from the latest technology.

You can get more information about how to use IronPDF for Java from our Code Examples pages.

IronPDF is free for development and can be licensed for commercial use. For more information about the license, visit the following link.