Welcome to the Ranch.
The only line where anything is changed is line 105 - have you ensured (via logging) that that is actually executed?
The output at line 107, at least on the surface, seems to make me believe I changed the field value... at least in memory.
I am not familiar with "logging", if you would be so kind, could you expand on that a bit?
But line 105 is not executed every time line 107 is executed, due to the if statement around the former.
Not sure what is going on, but the entire logic seems rather roundabout, what with looping through all fields. It seems you could replace lines 61 to 65 (and thus the entire processField method) with a few lines of code as shown in https://github.com/apache/pdfbox/blob/trunk/examples/src/main/java/org/apache/pdfbox/examples/fdf/SetField.java, starting in line 49.
I don't think I understand. You do have the name - it's "form1.Page1.SEND_TO".