how can I make my form accept pdf submission documents?

I see the form already accepts "doc," "jpeg," etc. But I would like it to accept "pdf" format submissions as well. When they fill out the form, at the bottom they can "upload" a document to accompany it.

How do I set this up?

You can indeed change the allowed file types:

https://www.jotform.com/help/29-Upload-Field-Allowed-File-Types

The maximum file upload size can also be increased.  Here is our quick guide detailing how to increase the limit as well as the maximum file sizes for different integrations:

https://www.jotform.com/help/33-Changing-the-Upload-Size-Limit