I'd like to include a contact form, specifically for a client to upload a file during the checkout process and only have the files passed thru if the

Thank you for contacting us. I also recommend creating an account first.

You can sign up using your email account at https://www.jotform.com/signup

As to your question, your message was cut off and was missing details.

Can you please complete the message and resend again using this link https://www.jotform.com/answers/1792762

Let us know if you need further assistance.

Also, I'm using a website builder so am limited to html code in a field, or PayPal button variables  

Based on your requirement, I understand that you want to let the user upload the files only if the payment is successful. If so, you may consider creating two separate forms, one for the payment and the other for uploading the files. Once the payment is done on the first form, it can be redirected to the second form by using the Thank you page.

https://www.jotform.com/help/38-Redirecting-Users-to-a-Different-Page

Hope this information helps! Please give it a try and let us know if you need any further assistance. We will be happy to help.