I found the documentation on how to use custom field merge tags to display an advanced custom field value from the post/page the form was submitted from.
Now I would like the form to be submitted from another page. More specifically: If someone clicks on a sign-up button on a single post, I want them to go to another page (sign-up-page) which holds the form, and retrieve the custom fields data of that particular post (i.e. the previous page they came from) to display in the form.
If you feel you need assistance implementing this, we would recommend contacting a freelance developer. Gravity Forms areofficial partners withCodeable, who are the #1 WordPress outsourcing service. They can provide quality development from hand-picked Gravity Forms specialists for any project size and budget. Additionally, they can also provide you with a no obligation estimate of what the project may cost up front. You can reach them via this link.
You can also post to our Community Forum Job Board, We do not vet any of the individual developers there, it is an open forum for all, but our community is certainly full of talented folks!