How to Convert DOCX to PDF in Java

Ever since its introduction in Microsoft Word 2003, DOCX format has always maintained a high prominence in offices worldwide due to its easy editing and deep levels of design choices. Its limitations do start to show when it comes to compatibility, and especially consistency of viewing for the end user. Its complexity quickly becomes a liability, with varying versions of compatible applications resulting in unintended (and often unfortunate) consequences for your painstaking designs. On the opposite side of things, you have PDF, with its ubiquitous support and unshakably consistent display fidelity, no matter the device, operating system, or app. Unfortunately, PDFs are also notoriously impractical when it comes time to make edits.

As a result of these individual strengths and weaknesses, converting between these two formats remains very necessary and often crucial in many cases. While it might be a simple matter to manually converting a handful of DOCX files into PDF format, this is certainly not the case when a more automatic approach is required. Approaching this conversion from a programmatic perspective, there are many problems that have to be solved. 

Our primary issue is the matter of parsing the DOCX file to begin with. The main reason for this is that DOCX is immensely complicated. The ECMA specifications for this format comprise a staggering 5,000 pages, with new features being added regularly. Once again, the sheer depth of choice in DOCX returns as a double-edged sword. Another problem is the fact that DOCX files are actually zipped archives containing multiple metadata and document files. Sorting the relationships between these files using “rels” is certainly no easy task. And we still have not even addressed the matter of converting all of this parsed data into the final PDF.

Let us assume that you do not have the development time or budget to grind through this whole process from scratch. This tutorial will show you how to solve this dilemna by using a cloud-based API to perform our conversion from DOCX to PDF.

We will also cover how to use this API to perform search and replace operations on DOCX files. Performing search and replace programmatically for a DOCX file is actually surprisingly difficult, running directly into the previously mentioned parsing issues. Thankfully our API can perform this task for us as well. Putting this all together will allow us to use the editing power of DOCX to easily create rich text templates for reports, invoices, letters, etc, populate them with search and replace, and then convert them to PDF format. Thus, we can use the strengths of DOCX to compensate for the lack of editing options in PDF.

Our primary goal in today's demonstration will be to maintain the maximum level of fidelity in our conversions. Important design choices such as page layout, tables, and annotations will all remain intact. With that said, let us get started with our setup process.

Our first step covers installation of our API client. Let us add a repository reference to our Maven POM file, like so:

<repositories>

    <repository>

        <id>jitpack.io</id>

        <url>https://jitpack.io</url>

    </repository>

</repositories>

That will allow Jitpack to dynamically compile our library after we add the following dependency reference:

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<dependencies>

<dependency>

    <groupId>com.github.Cloudmersive</groupId>

    <artifactId>Cloudmersive.APIClient.Java</artifactId>

    <version>v3.62</version>

</dependency>

</dependencies>

With our library compiled, we can now proceed with implementing it into our controller. Simply add these import commands to the beginning of our file.

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// Import classes:

//import com.cloudmersive.client.invoker.ApiClient;

//import com.cloudmersive.client.invoker.ApiException;

//import com.cloudmersive.client.invoker.Configuration;

//import com.cloudmersive.client.invoker.auth.*;

//import com.cloudmersive.client.EditDocumentApi;

Now it is time to call our first function, in this case convertDocumentDocxToPdf. Below is some example code, demonstrating how to structure this.

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ApiClient defaultClient = Configuration.getDefaultApiClient();

// Configure API key authorization: Apikey

ApiKeyAuth Apikey = (ApiKeyAuth) defaultClient.getAuthentication("Apikey");

Apikey.setApiKey("YOUR API KEY");

// Uncomment the following line to set a prefix for the API key, e.g. "Token" (defaults to null)

//Apikey.setApiKeyPrefix("Token");

EditDocumentApi apiInstance = new EditDocumentApi();

ReplaceStringRequest reqConfig = new ReplaceStringRequest(); // ReplaceStringRequest | Document string replacement configuration input

try {

    byte[] result = apiInstance.editDocumentDocxReplace(reqConfig);

    System.out.println(result);

} catch (ApiException e) {

    System.err.println("Exception when calling EditDocumentApi#editDocumentDocxReplace");

    e.printStackTrace();

}

While not particularly complicated, it is important to follow some requirements here:

• A valid DOCX document should be used as our inputFile
• Our function must be called from an API instance
• Use an API key, which can be obtained for free from the Cloudmersive website. This key is free, valid forever, limits input files to 4MB, and allows 1,000 API calls from any Cloudmersive API.

With that done, we have finished with our setup for DOCX to PDF. If you give it a test run, you will see that we can already start converting documents in real time. 

Now let us turn to the matter of using DOCX templates to create rich text PDF documents. Search and replace is the perfect tool for dynamically replacing fields to populate these templates. For a single search and replace operation, we can use editDocumentDocxReplace, which will take in a ReplaceStringRequest object. This is comprised of an inputFile (either through byte array or URL), a matchString to be searched for, a replaceString, and the matchCase bool, which determines if letter case is taken into account. Here is some example code you can use as reference:

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ApiClient defaultClient = Configuration.getDefaultApiClient();

// Configure API key authorization: Apikey

ApiKeyAuth Apikey = (ApiKeyAuth) defaultClient.getAuthentication("Apikey");

Apikey.setApiKey("YOUR API KEY");

// Uncomment the following line to set a prefix for the API key, e.g. "Token" (defaults to null)

//Apikey.setApiKeyPrefix("Token");

EditDocumentApi apiInstance = new EditDocumentApi();

ReplaceStringRequest reqConfig = new ReplaceStringRequest(); // ReplaceStringRequest | Document string replacement configuration input

try {

    byte[] result = apiInstance.editDocumentDocxReplace(reqConfig);

    System.out.println(result);

} catch (ApiException e) {

    System.err.println("Exception when calling EditDocumentApi#editDocumentDocxReplace");

    e.printStackTrace();

}

So what if you need to replace a large number of strings at once? Instead of calling the previously mentioned function repeatedly, we can instead make use of editDocumentDocxReplaceMulti. This function also takes in a request object, which contains an array of individual string replacement requests, each with its own matchString and replaceString. This allows rapid string replacement, making it particularly useful when combined with DOCX templates. For example, you could populate all of the various fields in a form with values such as names, addresses, and dates, all in real time with a single function call.

In this same library, you can also find functions for identifying and populating PDF form fields, retrieving and editing metadata, file validation, and conversions between numerous popular file formats.