The difficulty of "images" can arise as pdf files can use both text and images - if you scan a document and just bung the resultant "image" into a pdf file, it's effectively a "picture" as you would take with a camera (could be a black and white teapot as far as the computer's concerned) SO if that's the case you could probably copy and paste that image as an "image", but it wouldn't be editable in the sense of being able to alter the text in any way - which is where "OCR" comes in - high end scanners used to include it, so that it would effectively "read" the image when scanned, and spit out proper text. If you have a pdf file with an image of text, you may be able to get editable text by using OCR (there are several free downloadable programmes). It can be pretty effective, but it's a bit like using Google translate, you'll need to check it thoroughly for pigdin English!