Developing a Document Templating Engine for Word in C#
As a developer using .NET 8, automating complex, legally required documents in Word can be challenging. This guide details how they built a custom templating engine using Content Controls (SDT) to dynamically handle intricate templates like tables, images, and conditional sections.
Key points
- Work with complex structures outside of text using Content Controls (SDT).
- Sminex.DocxProcessor is a custom NuGet package built atop DocumentFormat.OpenXml.
- Keep the template file read-only and perform all modifications on a MemoryStream for safety.
- Achieve conditional rendering by deleting entire table structures or pages when no data is present.
- Integrate ImageSharp for image handling and manage pixel/size conversion using Word's internal EMU unit.
- Prevent unnecessary data access by using the Lazy<T> pattern in your DTOs.
The Sminex team developed a custom C# engine, Sminex.DocxProcessor, to manage structural Word document templates using Structured Document Tags (SDT/Content Controls). The core challenge was overcoming Word's complex XML structure which easily breaks when handled by simple text replacement logic. This new approach ensures that the original Word formatting remains intact while enabling developers to dynamically insert data and clone structural elements like tables or images.
The engine handles the template as read-only, performing all operations on a MemoryStream to ensure thread safety and file integrity. Furthermore, it supports conditional rendering by allowing the entire structure of a table or even a page to be removed if no data is provided. This effectively brings a form of conditional formatting to Word, allowing template creators to maintain visual design while developers manage the logical content generation.
Real-world use
- Automating officially formatted contracts and legal reports requiring fixed structure.
- Generating automated inspection reports detailing damage points marked on photos with structured lists.
- Creating dynamic forms where entire sections (like supplementary photo logs) are included or excluded based on data presence.
- Placing customer data such as names and authorization details into specific sections of a complex template based on business logic.
Why it matters
This engine eliminates manual errors in legally bound documents while maintaining Word's unique formatting capabilities, allowing for true automation without sacrificing visual fidelity.