TypeLoadException Due to Version Mismatch in DocumentFormat.OpenXml

[vaceslav]

Description

I am using the NuGet package DocumentFormat.OpenXml version 3.2.0 in my project. However, when I attempt to read my template file, I encounter the following exception:

System.TypeLoadException: Could not load type 'DocumentFormat.OpenXml.OpenXmlElementList' from assembly 'OpenXMLTemplates, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' due to value type mismatch.
   at OpenXMLTemplates.OpenXmlExtensions.DescendantsBreadthFirst[T](OpenXmlElement element)+MoveNext()
   at OpenXMLTemplates.OpenXmlExtensions.ContentControls(WordprocessingDocument doc)+MoveNext()
   at OpenXMLTemplates.Documents.TemplateDocument..ctor(WordprocessingDocument wpd)
   at OpenXMLTemplates.Documents.TemplateDocument..ctor(String filePath)
   ......

Cause

This issue occurs due to a version mismatch between DocumentFormat.OpenXml dependencies. The project is currently using DocumentFormat.OpenXml version 3.2.0, but it appears that OpenXMLTemplates is built against an older version (2.9.1), leading to compatibility issues.

Proposed Solution

To resolve this issue, OpenXMLTemplates should be updated to use DocumentFormat.OpenXml version 3.2.0 instead of 2.9.1.

[vaceslav]

FYI for anyone landing here: this repo has been inactive for 2–3 years, so I ended up building an alternative — Templify, a .NET 10 library for the same use case (placeholder replacement in .docx without MS Word, plus conditionals, nested loops, tables, and markdown in values). It's open source (MIT) and actively maintained.

Full disclosure: I'm the author. Sharing in case it's useful to others who hit the same limitations I did.