Can’t attach a file while filling out a PDF form. Clicking “Add Attachment” button doesn’t wor

I’m filling out a PDF as an end user. I have been instructed to use Acrobat *READER*, not Acrobat Pro.

The PDF has a button that says “Add Attachment.” Clicking this button does nothing. How do I add the attachment?

I do NOT want to use Acrobat Pro to embed the attachment somewhere else, as I do not want to confuse the form provider. I’ve never seen this before. What do I do?