I have a .png image file (Company logo) that I want to include on the pdf file attached to the autoresponder email

To show an image in the PDF, you can either add the image to the form and include headers, text and images from the form in the PDF:

https://www.jotform.com/help/305-How-to-Show-Headers-and-Text-in-the-PDF

Or edit the PDF output directly to include the image:

https://www.jotform.com/help/384-How-to-Customize-PDF-Submissions-Report

I have the image in a folder on my mac but don't understand how to add to pdf, it asks for a URL

If you are adding it to the PDF directly, you would indeed need to image to be hosted elsewhere.  There are many free services like Imgur that allow for hosting images:

https://imgur.com/