Yes, they can, and the postscript portions are even stored in plain text for you to edit, unless you tell whatever pdf compilation tool you're using to encrypt

Yes, they can, and the postscript portions are even stored in plain text for you to edit, unless you tell whatever pdf compilation tool you're using to encrypt the entire document. There is no conversion unless you're using a poorly written PDF compiler. (this also makes your analogy pretty weak - it's more like "having a PNG include a bitmap image", in addition to all the other data it can contain) of course, most _readers_ will ignore raw postscript because the PDF format is intended for print documents and having an insanely complex code instruction that draws "a picture" is crazy inefficient compared to just including the vector graphic (not the bitmap graphic, that would be quite dumb) that the postscript program is supposed to yield.