We need a bit more information: What version of Acrobat are you using, and on what operating system?
How are you trying to sign the form? What exactly happens when you do that?
Does the form have a signature field in it? Is the PDF file protected? You can find out by bringing up the document properties (Ctrl-D or Cmd-D), and then go to the "Security" tab. Are there any limitations listed?
I'm on a MacBook (Sierra - 10.12.1) and Acrobat Reader Version 2015.020.20042
When I click sign I get a message sayinng 'This document is a fillable form and does not let you drag or drop saved information'
Can't get any further than that. I tried looking through the forums and I couldn't find an answer that worked for me.
Thank you so much! I didn't see that...