PDF is an image description format, nothing more.
Um, wrong. PDF is a subset of Postscript, and it can contain text (rendered in the native system's fonts) as well as image data. It can also contain "marked-up" portions of the image, that are rendered as images, but have text associated with them (so you can copy and paste outside the PDF by selecting a part of the image as you would a block of text).

Score:2, Informative