PDF requires an external application like Adobe Acrobat Reader (or any other free variants) while JPEG does not. An external application comes with the handicap of loading times. Plus the rendering of a PDF document happens only after the complete document is downloaded while images can be streamed in. You need to convert PDF to JPEG format. Here I would recommend you MicroPDF PDF to JPG Converter!
This professional program can help you convert PDF to JPG/JPEG, PDF to TIF/TIFF, and PDF to PNG, PDF to BMP, etc. in a few steps. The original text, pictures and layout are still accurately preserved. With this software, you can convert unlimited PDF files at one time, or choose Partial conversion as you like. You can also set output color as colorful, black/white or gray and resolution. Besides, it supports converting encrypted PDF in multiple languages.