Your description suggests your form uses content controls, presumably in a document with 'filling in forms' protection applied. That you're getting stuck on checkboxes suggests you're also using formfields. You really shouldn't use content controls and formfields in the same document, as they're not designed to work together.

As for the locking, that could be implemented via a content control on exit macro, or via a Document_Open macro, but you'd need to do this carefully, so as to not lock the form or a given content control prematurely.

Without seeing the form and knowing more about your requirements, it's difficult to provide more specific advice. You can attach a document to a post (delete anything sensitive) via the paperclip symbol on the 'Go Advanced' tab at the bottom of this screen.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]