How do you upload a pdf to the form?

Do you mean you want to display a PDF to your form? You can use the PDF Embedder widget to achieve your requirement. Here's the link: https://widgets.jotform.com/widget/pdf_embedder. 

If you mean you want your users to upload their PDF files to your form, then you can follow this guide to add an upload field to your form: How to Create Upload Forms.

Please let us know if you need further assistance.
Regards.