Great question! While we do offer the option to create an email directly from a PDF, the good news is you can also manually create an email with your own image. Your can upload images to your Library whether they are JPGs, PNGs, and GIFs. Once your image is uploaded it can then be added into your email. I do however want to also point out it's important to not send emails that are completely images. Having a good balance of text, images, and links will help maximize your email deliverability rate. Sending emails made completely of images can cause it to get caught in spam filters.
You will want to grab the blue box with a white arrow at the bottom right-hand corner of the PDF to stretch it across the whole template.