Low resolution of JPG when using PDF to JPG?

When you export to JPEG, the fiel save dialog has a "Settings" button. When you click on that, you can select the output resolution. Also, if you want to always use a higher resolution, you can go into Acrobat's preferences, go to the "Convert from PDF" category and then select JPEG. You will get the same dialog as before, but now you are setting the defaults for this export function.