some of the fields in my form are not showing up on the PDF file in Dropbox

Please see attached screenshot

From the submission view of your form, under the "More Settings" menu, make sure all form fields are checked:

https://www.jotform.com/help/269-How-to-View-Form-Submissions

If the fields are not selected in that menu, they will be omitted from the PDF output, including the PDF sent to Dropbox.