Send a PDF as an attachment using Mail (2) Form

Hello,
I have a website that has some popups to gather e-mails from users. In the popup, there is a contact form that uses the Mail (2) feature to say thank you to the user. Right now, I just include a link to the PDF for them to download. I was wondering If when they receive the thank you email if I could attach the PDF as an attachment instead of just giving a URL to the PDF. I know there is a “File Attachments” section in the Mail (2) portion of the contact form but I haven’t been able to get it to work no matter what file path I use for the PDF.