Converting Word Documents to PDF in .NET Core Without Microsoft Office Interop

Converting Word documents (.doc and .docx) to PDF format in a .NET Core environment can be challenging, especially when you need to avoid using Microsoft Office Interop. This article explores various methods and tools available to achieve this conversion, focusing on open-source and cross-platform solutions.

The Challenge: .NET Core and Office Interop

Traditionally, converting Word documents to PDF involved using Microsoft Office Interop. However, this approach has limitations, particularly in .NET Core applications:

• Dependency on Microsoft Office: Requires Microsoft Office to be installed on the server, which might not be feasible in cloud or containerized environments.
• Platform Restrictions: Office Interop is primarily designed for Windows, limiting cross-platform compatibility.
• Licensing Costs: Using Microsoft Office on a server may incur additional licensing fees.

Solutions for .NET Core Word to PDF Conversion

Fortunately, several alternative methods can be used to convert Word documents to PDF in .NET Core without relying on Office Interop.

1. Open XML SDK and HTML Conversion

This approach involves using the Open XML SDK to read the content of the Word document (.docx) and transform it into HTML. Then, an HTML to PDF converter is used to generate the final PDF file.

Steps:

1. Open XML SDK: Utilize the Open XML SDK to access the content of the .docx file. This SDK now supports .NET Standard, making it compatible with .NET Core.
2. Docx to HTML Conversion: Employ a library like Open-Xml-PowerTools to convert the .docx content into HTML. A .NET Core version of this tool is available, enabling this conversion in cross-platform environments.
3. HTML to PDF Conversion: Use an HTML to PDF converter library such as DinkToPdf, a cross-platform wrapper around the Webkit HTML to PDF library libwkhtmltox, to convert the generated HTML into a PDF document.
   • Ensure libwkhtmltox.so and libwkhtmltox.dll are in the project root for Linux and Windows compatibility.
   • Install libgdiplus on your Linux machine or Docker image, as libwkhtmltox.so depends on it.

Advantages:

• Cross-platform: Works on various operating systems, including Linux and Windows.
• No Office Interop: Eliminates the dependency on Microsoft Office.
• Customizable: Allows fine-grained control over the conversion process.

Disadvantages:

• Complexity: Requires more coding effort compared to other solutions.
• HTML Conversion Issues: Complex Word documents with intricate formatting might not be perfectly replicated in HTML.

2. LibreOffice Binary

LibreOffice is an open-source office suite that can be used to convert documents to PDF. Since there's no official .NET API, you can interact with the soffice binary directly.

Implementation:

1. Locate LibreOffice: Determine the path to the soffice executable based on the operating system.
   • Linux: /usr/bin/soffice
   • Windows: <binaryDirectory>\\Windows\\program\\soffice.exe
2. Execute Conversion: Use ProcessStartInfo to execute the soffice command with the --convert-to pdf --nologo {0} arguments.
3. Error Handling: Check the exit code of the process for any errors during conversion.

Advantages:

• Wide Format Support: Supports various document formats beyond .doc and .docx.
• Open Source: Leverages a free and open-source solution.
• Fewer Bugs: Potentially fewer issues compared to rolling your own solution.

Disadvantages:

• "Hacky" Solution: Relies on direct interaction with a binary, which can be less robust than using a dedicated API.
• Filename Handling: Requires careful handling of filenames to prevent code execution vulnerabilities.
• Font Issues: May not render proprietary fonts correctly unless they are installed on the OS.

3. FreeSpire.Doc

FreeSpire.Doc is a .NET library that allows you to convert Word documents to PDF.

Implementation:

1. Install Package: Add the FreeSpire.Doc NuGet package to your project.
2. Conversion: Use the Spire.Doc.Document class to load the Word document and save it as a PDF.

Spire.Doc.Document document = new Spire.Doc.Document(wordFilePath, FileFormat.Auto);
document.SaveToFile(pdfFilePath, FileFormat.PDF);

Advantages:

• Easy to Use: Simple API for converting documents.
• Free Option: Offers a free version with limitations (e.g., a 3-page limit).

Disadvantages:

• Limitations: The free version has a page limit and might include watermarks.
• RTL Language Support: Does not properly support RTL (Right-to-Left) languages.

4. Gotenberg (Dockerized Solution)

Gotenberg is a Docker-based solution that provides an API for converting documents to PDF, including support for Word documents through LibreOffice.

Implementation:

1. Docker Setup: Set up a Docker environment and pull the Gotenberg image.
2. API Calls: Make HTTP requests to the Gotenberg API to convert documents.

Advantages:

• Stateless API: Easy to integrate into microservices architectures.
• Feature-Rich: Offers more features beyond basic document conversion.
• Self-Sufficient: Includes all necessary dependencies within the Docker container.

Disadvantages:

• Docker Requirement: Requires familiarity with Docker and containerization.
• Overhead: Docker adds overhead compared to a library-based solution.

5. Report-From-DocX-HTML-To-PDF-Converter

This is a free library under the MIT license that leverages LibreOffice to convert DOCX files to PDF.

Advantages:

• Free: Completely free to use.
• Uses LibreOffice: Relies on a well-established conversion tool.

Disadvantages:

• LibreOffice dependency: Requires LibreOffice to be installed.

Choosing the Right Solution

The best approach depends on your specific requirements and constraints:

• For cross-platform compatibility and no dependency on external software, the Open XML SDK and HTML conversion is a solid choice.
• If you're comfortable with Docker and need a stateless API, Gotenberg is a great option.
• For a simple and quick solution with a free option, FreeSpire.Doc can be useful, but be mindful of its limitations.
• If you need to support a wide range of document formats and prefer an open-source solution, using the LibreOffice binary directly is a viable option.

Conclusion

Converting Word documents to PDF in .NET Core without Microsoft Office Interop requires careful consideration of the available tools and techniques. By leveraging open-source libraries and cross-platform solutions, you can achieve this conversion efficiently and effectively, regardless of your deployment environment.