$ perl acroform.pl 
Text Box 1
MyTopSecretListBox

$ pdftk test.pdf dump_data_fields
---
FieldType: Text
FieldName: Text Box 1
FieldFlags: 0
FieldValue: 
FieldJustification: Left

$ pdftk new.pdf dump_data_fields
---
FieldType: Text
FieldName: Text Box 1
FieldFlags: 0
FieldValue: 
FieldJustification: Left
---
FieldType: Choice
FieldName: MyTopSecretListBox
FieldFlags: 0
FieldJustification: Left
FieldStateOption: Hidden item nobody will find
FieldStateOption: Item I'm very proud of
FieldStateOption: My sneaky item #1

$ pdftk new2.pdf dump_data_fields
---
FieldType: Text
FieldName: Text Box 1
FieldFlags: 0
FieldValue: 
FieldJustification: Left
---
FieldType: Choice
FieldName: MyTopSecretListBox
FieldFlags: 0
FieldValue: Hidden item nobody will find
But we are not limited to our silly list,
if value is set programmatically#10;
FieldJustification: Left
FieldStateOption: Hidden item nobody will find
FieldStateOption: Item I'm very proud of
FieldStateOption: My sneaky item #1