> From the forms menu I've added:
> form fields
[quoted text clipped - 8 lines]
>
> What am I missing?
Click the Design Mode button on the Control Toolbox to toggle into run mode.
Then you can lock the document.
Be aware that simply having any controls from the Toolbox in your document
is going to trigger the macro security stuff. If the user's security level
is High, they'll be stuck in design mode with no clue about why. If it's set
to Medium, they'll get the warning dialog with Disable and Enable buttons.

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Regards,
Jay Freedman
Microsoft Word MVP FAQ: http://word.mvps.org