Illustrator SDK :: Loop Through Layers And Determine If Its Text Layer

I am trying to loop/iterate through all layers, determine if it's a "text-layer", if it is, set it's opacity to 0.This is what I have so far:
 
                var iapp = new Illustrator.Application();
                var openoptions = new Illustrator.OpenOptions();
                var idoc = iapp.Open("c:\myFile.pdf", Illustrator.AiDocumentColorSpace.aiDocumentRGBColor, openoptions);
                Illustrator.Layer mainlayer = idoc.Layers["Layer 1"];
 [code]....