What is SVG?
SVG is a drawing rather than a grid of pixels: shapes, paths and text described in XML, so it stays sharp at any size. That makes it right for logos and icons and useless for photographs. Converting it to a raster format fixes the size it will ever be.
What is PPM?
PPM is a Netpbm image: a tiny text header giving the dimensions, then raw pixel values with no compression whatsoever. Almost nothing displays it, which is rather the point - it is what image-processing code and academic tools emit when they want to be trivially readable.