How to create PDF download gate

I have a custom field called "Brochure" which stores a link to an associated PDF. I want to enable users to download the PDF, but only once they've submitted their contact information. The functionality I want is the same that offered by this plugin: https://wordpress.org/plugins/email-before-download/ But this plugin is reliant on another one that manages downloads etc which is no good to me as I already have the PDF's uploaded and associated with posts using a custom field