There is no guarantee, especially if the object (annotation/field) can receive the focus. Also, different viewers may (and do) behave differently. In general though, when an annotation receives the focus, it will appear to be on top of any others.
Thanks for your reply.
When you say "In general though, when an annotation receives the focus, it will appear on top of any others", are you talking about when I'm EDITING my PDF?
I'm not concerned about editing my PDF, I'm concerned about what customers will see when they open the PDF. My document will be secured and the customer cannot edit it. Is there any way for me to specify that a certain annotation will appear on top of a certain field object? Or will annotations always be obscured by field objects?
Also, you indicated "different viewers may (and do) behave differently". I presume, by "viewers", you mean programs like Adobe Reader. In my case, the use of Adobe Reader and only Adobe Reader will be required.
Thanks for your further thoughts.
I was talking about when someone uses the document. I was mostly thinking about fields, as opposed to others types of annotations.
Z order is not a concept for annotations and form fields. Results are unpredictable, change between software and versions. If you want consistent display you must eliminate overlap.
Thanks for everyone's replies. I'm marking Test Screen Name's answer as the correct answer since it most clearly says there is no way to reliably ensure how overlapped annotations and form fields are displayed.