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Free Java API to Convert High-Quality Word Document to PDF

A Leading open Source Library Enables Java Developers to Convert MS Office DOCX, XLSX, and PDF Files With High Accuracy Using Native Applications.

What is Documents4j ?

documents4j is a powerful open-source Java library designed for converting documents between different formats, such as DOCX to PDF or XLSX to PDF. Unlike many traditional libraries, documents4j delegates the conversion process to native applications like Microsoft Word and Excel, ensuring high-quality output with minimal formatting issues. The library takes a different approach. Instead of re-implementing the conversion logic, it acts as a bridge, delegating the heavy lifting to native applications (like Microsoft Word or Excel) that already understand these formats perfectly. This ensures that the output document—such as a PDF generated from a Word file—looks exactly as it would if you had clicked "Save As" manually in MS Office.

The primary value of documents4j lies in its accuracy. For businesses that require professional-grade documentation where every margin and font must remain intact, relying on open-source parsers can be risky. documents4j is particularly useful for generating invoices or reports from templates, automating document workflows in a Windows-based environment and decoupling conversion logic from your main application through a remote server setup. By leveraging native applications, it ensures unmatched accuracy compared to traditional libraries. Its support for local and remote processing, concurrent execution, and load balancing makes it highly suitable for enterprise-grade systems.

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Getting Started with documents4j

The recommend way to install documents4j is via Maven repository. You can easily documents4j library directly in your Maven Projects with simple configurations.

Maven Repository for documents4j


// Here’s a commonly used dependency (Local converter): 

<dependency>
<groupId>com.documents4j</groupId>
<artifactId>documents4j-local</artifactId>
<version>1.1.13</version>
</dependency>

//If you only need the API:
<dependency>
<groupId>com.documents4j</groupId>
<artifactId>documents4j-api</artifactId>
<version>1.1.13</version>
</dependency>

Install documents4j GitHub


git clone https://github.com/documents4j/documents4j.git
cd documents4j
cd documents4j-local-demo
mvn jetty:run

Converting Word to PDF via Java Library

At the heart of documents4j is an elegantly designed fluent API that makes document conversion feel natural and readable. The IConverter interface provides a builder-style chain that lets you specify the source file or stream, declare input and output document types, set a conversion priority, and choose between synchronous or asynchronous execution — all in one clean expression. The API hides every implementation detail, so your business logic never needs to know whether a local or remote converter is running underneath. Here is a simple example that shows how to achieve the conversion process.

How to Convert Word to PDF via Java Library?

import com.documents4j.api.DocumentType;
import com.documents4j.api.IConverter;
import com.documents4j.job.LocalConverter;

import java.io.File;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

public class DocumentConverter {
    public static void main(String[] args) {
        // 1. Specify the source and target files
        File wordFile = new File("C:/documents/input.docx");
        File targetFile = new File("C:/documents/output.pdf");

        // 2. Initialize the converter (Local instance)
        IConverter converter = LocalConverter.builder()
                .workerPool(20, 25, 2, TimeUnit.SECONDS)
                .processTimeout(5, TimeUnit.SECONDS)
                .build();

        // 3. Execute the conversion fluently
        boolean success = converter.convert(wordFile).as(DocumentType.MS_WORD)
                                   .to(targetFile).as(DocumentType.PDF)
                                   .execute();

        if (success) {
            System.out.println("Conversion completed successfully!");
        }

        // 4. Always shut down the converter to release native resources
        converter.shutDown();
    }
}

Remote Converter with REST API Server

Not every Java application server has MS Office installed — nor should it. documents4j solves this with a built-in Remote Converter architecture. A standalone conversion server (which internally uses a LocalConverter) runs on a separate Windows machine with MS Office installed and exposes a REST API. Your Java application uses a RemoteConverter that sends documents over HTTP and receives the converted file back. The entire handshake is invisible to application code; the same IConverter interface is used on both sides.

How to Perform Remote Word Documents Conversion inside Java Aps?

import com.documents4j.api.DocumentType;
import com.documents4j.api.IConverter;
import com.documents4j.job.RemoteConverter;

import java.io.*;
import java.util.concurrent.TimeUnit;

public class RemoteConverterExample {

    public static void main(String[] args) throws Exception {

        // The RemoteConverter connects to the standalone server
        IConverter converter = RemoteConverter.builder()
                .baseFolder(new File("/tmp/documents4j"))
                .workerPool(10, 20, 5, TimeUnit.SECONDS)
                // Timeout for each HTTP conversion request
                .requestTimeout(30, TimeUnit.SECONDS)
                // URI of the running conversion server
                .baseUri("http://192.168.1.100:9998")
                .build();

        // Convert using InputStream / OutputStream — recommended for RemoteConverter
        // because data is already serialized for HTTP transport
        try (InputStream source = new FileInputStream("/input/contract.docx");
             OutputStream target = new FileOutputStream("/output/contract.pdf")) {

            boolean success = converter
                    .convert(source).as(DocumentType.MS_WORD)
                    .to(target).as(DocumentType.PDF)
                    .execute();

            System.out.println("Remote conversion success: " + success);
        }

        converter.shutDown();
    }
}

SSL Encryption and Basic Authentication

In production environments, document files often contain sensitive business, legal, or personal data. Transmitting them over plain HTTP is a serious security risk. The documents4j library addresses this with built-in support for SSL/TLS encryption between the conversion client and server, configurable via Java's standard SSLContext. The standalone server also supports HTTP Basic Authentication to ensure only authorized clients can submit conversion requests. Both security features can be enabled with minimal configuration, making documents4j a viable solution even in regulated industries.

Asynchronous and Prioritized Processing

Conversions can be resource-intensive. documents4j allows you to schedule conversions to run in the background (asynchronously) using a Future return type. Furthermore, it supports a prioritization mechanism. If your application handles a high volume of requests, you can assign a higher priority to critical documents to ensure they are moved to the front of the internal job queue.