RenderFileAttachment.cs

string outputDirectory = @"C:\output";
string pageFilePathFormat = Path.Combine(outputDirectory, "page_{0}.html");
MemoryStream attachmentStream = new MemoryStream();
 
using (Viewer viewer = new Viewer("sample.msg"))
    viewer.SaveAttachment("attachment-word.doc", attachmentStream); 
 
using (Viewer viewer = new Viewer(() => attachmentStream))
{
    HtmlViewOptions options = HtmlViewOptions.ForEmbeddedResources(pageFilePathFormat);
    viewer.View(options);
}