This puzzle was found in an old attic and was a religious invitation. Release the key and you could send it in to receive a Bible based book. Apparently 1000's were made but I can find no more other information about it, nor can I find the solution. Here's what I do know.
The 3 parts are made from completely different colors of paper so it could not have been manufactured from a single piece. This means that someone had to assemble it and it should be able to be undone. While the corners are worn, I inspected them closely and they have not been torn or cut. How can the key be removed? (Click for larger images)