Comparison between signatures via Reader / Pro

I need a security comparison of the following:

Scenario 1 - Using Adobe Reader I add a signature to a document.  The document does not have any fields and is not an electronic form.

Scenario 2 - Someone sends me an electronic form created using Adobe Pro. I click the signature field and sign it.

Does the signature in scenario one have the same digital information as the signature in scenario two?  What are the advantages of scenario 2 type signature over someone just adding their signature using Reader?

And finally, if someone adds their signature to a pdf document using Reader, does the file automatically lock down so that it can't be altered like it does with an elctronic form?

Background:

We have many documents that only require a signature and a date.  We need to know what the drawbacks are of not creating an electronic form with a digital signature field and just letting the recipient use Adobe reader to sign.