Newsletter sign up with opt in offer pdf

Site URL: https://amybaratta.com/

I'd like to add a pop up or newsletter block on my website that entices visitors to sign up for my newsletter and they will receive a free guide in the form of a pdf (they can download once I send them a welcome to my monthly newsletter email). It would go something like this: “Sign up for my monthly newsletter and I’ll send you a free sustainable shopping guide”!

 It seems a bit confusing on square space, I was told the email would contain a link that the guest could follow and grab the document from my site. Wondering if a third party like Mailchimp would be better for this than the SS email campaigns? I’m not even sure if I have a choice since I already signed up for the email campaigns : ( thx