How to Convert DOCX to DOC using C#. For more information, please follow link: https://kb.groupdocs.com/conversion/net/how-to-convert-docx-to-doc-using-csharp/

How to Convert DOCX to DOC using C#.cs

using GroupDocs.Conversion;

namespace ConvertDOCXtoDOCUsingCSharp
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Set License to avoid the limitations of Conversion library
            License lic = new License();
            lic.SetLicense(@"GroupDocs.Conversion.lic");

            // Import DOCX document 
            var converter = new GroupDocs.Conversion.Converter("input.docx");

            // Get conversion option for final output document
            var conversionoptions = converter.GetPossibleConversions()["doc"]
                .ConvertOptions;

            // Save the DOC to disk
            converter.Convert("output.doc", conversionoptions);
        }
    }
}