GeneratePreview

public void GeneratePreview(PreviewOptions previewOptions)

using (Metadata metadata = new Metadata(Constants.InputDocx))
{
    PreviewOptions previewOptions = new PreviewOptions(pageNumber => File.Create($"{Constants.OutputPath}\\result_{pageNumber}.png"));
    previewOptions.PreviewFormat = PreviewOptions.PreviewFormats.PNG;
    previewOptions.PageNumbers = new int[] { 1 };

    metadata.GeneratePreview(previewOptions);
}