Since GroupDocs.Viewer update 21.8 it seems no longer possible to use GroupDocs.Conversion in the same project.
If you open the attached solution and try to convert the attached file, you will see the “FatalExecutionEng…...sure to restore the NuGet packages and adjust all file paths...csproj On line 64: <HintPath>..\packages\GroupDocs.Viewer.21.8.0\lib\net40\GroupDocs...