When signing a document, signature is hidden behind stamp\pasted image

Hello, 

In both Adobe Pro and Adobe reader we use stamps in order to create an area where staff can sign a document\add a date and any additional comments. Users are able to paste the stamp, but when they try to place there signautre on the stamp, it goes to the layer behind the stamp. I've been unable to find a way bring the signature to the front. I figued flattening would resolve this, but it does notthing.