A digital signature can wrap the digital image or collection of data so that any change to the document cancels the signature just as cutting and pasting invalidates a paper document after it is signed. Simply pasting the image of a signature onto an email would not be, by statute, a valid signature. So, be sure your digital signature use meets the Statute, the Administrative Rules and the practices and standards defined by GITA and the Secretary of State's Office. Using PKI does identify who the party is but that is not the same as them formally signing something. So it is confusing to describe every PKI use as a digital signature use.
Vendors commonly use the terms interchangeably.
But what is sold is not necessarily a valid digital signature use for Arizona government. Conversely, there is often a distinction made between digital signatures and electronic signatures. Again, this a distinction of more value to the vendor than to the business person using the technology. It's a little like saying I drive a diesel car or a gasoline car when what might be more important is that it is a car and how many seats it has. The Statute establishes specific tests for correct electronic signature use.