I have added a link to a great ImageMagick examples page in the documentation. You can recognize that you need the Read method when you see a colon in the examples and no file is being read. For example this:
convert.exe caption:'ImageMagick Rules OK!' caption_centered.gif (http://www.imagemagick.org/Usage/text#caption)
convert.exe rose: rose.png (http://www.imagemagick.org/Usage/files/#special_formats)using (MagickImage image = new MagickImage("image.tif")) { using (MagickImage text = CreateCaption("caption:Magick.NET")) { // http://www.imagemagick.org/Usage/compose/#over image.Composite(text, 50, 50, CompositeOperator.Over); } }