I am not sure what you want to achieve. Do you want to convert pdf to image or a scanned image to PDF? And do you want to manipulate the PDF or the image? That will make a difference in the solution.
Either way i think you will need a third party java library to do so.
Check out https://stackoverflow.com/questions/4886042/pdf-to-image-using-java for example.
Aspose also offers enterprise quality libraries for such actions, but that comes with a price tag.