Download multiple PDF's from pop-up or form.

Site URL: https://hawk-burgundy-4876.squarespace.com/construction-typologies

Hello,

I would like to create a pop-up or form that would require visitors to subscribe before downloading PDF brochures. I would like to have checkboxes that would let them decide what PDFs to download, since I would like to avoid having separate pop-up with a sign-up form for each brochure. I've mahaged to create the form, but I'm struggling to write a code that would make it work. Is such a thing even possible in Squarespace?  

Here is a link to a page:

https://hawk-burgundy-4876.squarespace.com/construction-typologies

Any help or suggestions would be greatly appreciated.

Seba