Salesforce and Sign - initial simple document setup question

Hello,

I need to know how to designate signage field location on an existing pdf.  There is functionality to do this by checking off the checkbox entitled "Preview document or position signature fields" (screen cap included), but we need to not have to do this each time we send an agreement.  I spoke with an Adobe tech support rep who told me that the pdf needed to be setup in acrobat first in order for this to be recognized from within Salesforce and Sign.  But my attempt to do so simply resulted in additional fields, not designation of where the signage fields are to go. 

Please help by explaining where this sort of setup is conducted, in Acrobat, in one of the Sign Salesforce modules, or elsewhere.

Thank you in advance,

WD