What is wrong with my Batch Processing Script to Auto Size Text for two fields in 5000+ PDFs

Hello!

I have 5000 + PDFs and I need to make the text size "Auto" for two specific fields in many PDFs and to save them without a prompt. I can't find the solution anywhere. I use Adobe Acrobat DC and the files I need to edit are stored locally.   Here's what I have tried. Can someone edit my script?  It is not resizing the fields and I am being prompted to save each one rather than the "Save" function happening automatically.

Here are samples of what I tried  that don't work. This gives you a clue as to how amateur I am  :-):

var f = this.getField("HHMember9-Ethnicity-5")
f.readonly = false
f.textSize = Auto
f.readonly = true

var f = this.getField("HHMember8-Ethnicity-5")
f.readonly = false
f.charLimit= 3;
f.textSize = Auto.size
f.readonly = true

I wonder if the character limit is overriding the text size, or if I am just using the wrong