Fonts - Introduction to 3D Game Programming with DirectX 9.0 - page 159

Then you can render the 3D text mesh by simply calling the mesh's
DrawSubset method:
Text->DrawSubset( 0 );
9.4 Summary
Use the ID3DXFont interface to render text when you need to
support complex fonts and formatting. This interface uses GDI
internally to render text and therefore takes a performance hit.
Use CD3DFont to render simple text quickly. This class uses tex-
tured triangles and Direct3D to render text and is therefore much
faster than ID3DXFont .
Use D3DXCreateText to create a 3D mesh of a string of text.