What's available depends on the PDF. For example, if the form has usage rights applied (Reader-enabled), the EchoSign e-signature tools won't be available. There are other conditions as well, such as the existence of any digital signature fields, security restrictions, etc. What does it show for the security restrictions summary when you select: File > Properties > Security
That is what it would look like for a form that has been Reader-enabled. If you have Acrobat, you can remove the usage rights by selecting: File > Save a Copy
The resulting file can then be e-signed in Reader if it doesn't contain any digital signature fields.