Hello @SeattleChaineDesRotisseurs ,
Correct, that is how it works. Since we generally don't advise sending image-only emails, and since PDFs can't be embedded into emails, our system only generates an image of the first page in the scenario you wish to use it as a cover / preview image, to get your contacts to click and view the full document.
If you'd like to have all a PDF's pages converted into images, we'd suggest using either the program it was created in or another 3rd party program / site to convert those other pages, then upload the images into your Library. Just as a reminder, links from PDFs are not maintained in the image conversions, so if your PDF has multiple links, you'd still need to have the images of the pages redirect to the actual PDF document.