We implemented this for two of our customers. They basically wanted their form fields reformatted into a template that looks more like a personal message. For example, if the user populates the Customer Name, Customer Email and Date fields, the PDF they get shows something like,

Dear Customer Name,

We wanted to let you know that we are scheduled to come on site on <Date>. We will send you another email at <Customer Email> 24 hours before arrival.

Best,

<User Display Name>

Using Workflow to enter these fields into an email wasn't an option because there were also other elements on the form that the customer needed to see (e.g. user submitted photos needed to be embedded on the form), so it HAD to be the PDF.

Long story short, you can do this in a few steps:

1. Create a second form (call it "Template Form" or something)
2. Place the variables for the data you need from the original form
3. Use JavaScript to take the field values and combine them into one string.
4. Append the string somewhere on the form (perhaps into a Custom HTML field)

For example, it might look something like this:

$(document).ready(function() {
    var customerName = $("#Field1").val();
    var inquiryDate = $("#Field2").val();
    var myMessage = "Dear " + customerName + ",<br><br>We received your inquiry on " + inquiryDate +". We appreciate your business and...";

    $("#Field3").append(myMessage);
});

Then you add a Save to Repository activity in your process and save this second form with it, and the resulting PDF should have the message in the format you want. (You may also want to hide the fields you entered into the form as variables so the customer only sees the custom message.)