Problem Resolved: Formidable conflict with PDF Embedder Secure plugin
In response to my report of the conflict between plugins, you wrote "If the PDF Embedder author adds type="button" to all the buttons in
the PDF Embedder, then this will resolve the submit issue."
I sent this to Dan Lester, developer of the PDF Embedder plugin. He made the change you suggested, and it has solved the problem.
Thanks so much for your help with this!