I want to send a unique auto response email for each PDF link.

What if I have multiple PDF links? I want to send a unique auto response email for each link.

You can achieve this by using Conditions Email. 

You can setup your form to send an auto email that is base on a conditions rules (i.e. send an email base on a selected response in the form)

Review the user guide here: How-to-Send-Email-Based-on-Selection

Let us know if you need further assistance.