Save SVG to Png don't display Text

Open mermaid live editor, the Sample Flowchart Chart is opened and displayed.
Use Action=>SVG download to produce a SVG file.
Use the code:

      var svgDocument = SvgDocument.Open(strFullPath);
      var pngImage = svgDocument.Draw();
      pngImage.Save("MyExportedFile.png");

The PNG produced do not contain any text.

Any suggestions ?

Regards.