I've got the editable part down and it seems to be multi line but as you type into the field the height of the field stays the same and the font just gets smaller.
doc.text(20, 220, "Notes:");
var notesField = new TextField();
notesField.multiline = true;
notesField.maxFontSize = 12;
notesField.height = 150;
notesField.Rect = [280, 202, 160, 18];
notesField.fontSize = 12;
doc.addField(notesField);
This works for creating a multiline box with a fixed height. I haven't figured out how to create one with a dynamic height yet.
doc.text(20, 220, "Notes:");
var notesField = new TextField();
notesField.multiline = true;
notesField.maxFontSize = 12;
notesField.height = 150;
notesField.Rect = [280, 202, 160, 148];
notesField.fontSize = 12;
doc.addField(notesField);
doc.line(280, 200, 440, 200);```