JPG
JPG, also known as JPEG, is a file format that can contain image with 10:1 to 20:1 lossy image compression technique. With the compression technique it can reduce the image size without losing the image quality. So it is widely used in web publishing to reduce the image size maintaining the image quality.
PDF is a document file format that contains text, images, data etc. This document type is Operating System independent. It is an open standard that compresses a document and vector graphics. It can be viewed in web browsers if the PDF plug-in is installed on the browser.