Scripts embedded within a document cannot access the security settings of the document, so the simple answer is "you can't".
If you're not using certifying signatures then you could retrieve the PDF from the third manager, remove the security (as you alone know the password), delete the pages and re-apply it; but doing so will of course break a certifying signature. It's also possible to achieve a similar effect by hiding the pages - but to do that requires LiveCycle Designer templates and XFA forms, rather than PDF forms. It's not trivial but it does work, and there are some discussions about how to do it on the AcrobatUsers.com forums.
As Dave said, you can't delete pages from a signed file regardless of the encryption status. It would break the signature, be it a certifying signature or a regular approval signature. When someone applies a digital signature to a document they have the reasonable expectation that the fidelity and integrity of the document will remain unchanged post singing if their signature is going to remain valid. Removing a page definitely will violate those rules, thus that functionality is blocked in the signed file.
You know that the pages you want to remove aren't really part of the signed data, but Acrobat doesn't know that. The instruction pages were signed just as the meat and potatoes portion of the document was signed and they get the same protection.
Thank you all for trying to help. I guess I will have to live with the form as it is