If there is no PDF connected to your Template your screen will look like the screenshot below. Once you start mapping PDFs, you will have the option to select an existing PDF. File size limit is 10 megabytes (MB)
Visual Editing
Once you select a PDF or Multiple PDFs you can edit the PDF in the Visual Editing Step
Deleting a PDF
If you want to delete the current PDF connected to your template you can do that in the Settings Tab
If you need to compress, unlock, or prepare a PDF before uploading to Under, here is a link to ilovepdf.com