Signature Preferences in Reader X

Hi all -

I can't figure out how to turn this option off. Initially I thought it was an issue with how the PDF was being created when exported in InDesign CS6, but I can't find a security preference that matches this. I haven't set any requirements for signatures when creating the PDF.

When this document is opened in Acrobat, any changes made -- in this case, ticking checkboxes -- can be saved.

When this document is opened in Reader X, any changes made can't be saved. I receive the following prompt:

As most of my clients use Reader and not Acrobat, this is an issue. Can anyone point me in the right direction for how to fix this?

Thanks!

Erin