FlashVars pass field text to swf

I want to pass text to it from an acrobat field
If I put this in the FlashVars it works

myFlashVar=test

But I want to place text from a field in the pdf

var GuestNames = this.getField("Names");
myFlashVar = (GuestNames)

But I can't get it to work
Can it be done?

Can anyone help
Thanks