email before download

Hi there,

Would you please recommend the plugins for email before download that is compatible with the Highend Theme. I have found the below plug-ins for general wordpress.org, but I don’t know if they are compatible with Highend Theme.

Email Before Download: https://wordpress.org/plugins/email-before-download/
Contact Form 7: https://wordpress.org/plugins/contact-form-7/
Download Monitor: https://wordpress.org/plugins/download-monitor/

Also these can create the “email before download” function on a separate post; however, how can I add the function on an existing page?

Thank you.