Your document uses formfield checkboxes. For these to work by clicking on them, you need to apply the 'filling in forms' editing restrictions to the document. Doing so, though, will render the rest of the document uneditable - you'd need to add text formfields to any parts of the document where you want to allow user input.

As an alternative, you could use a checkbox content control (Office 2010 & later) or a dropdown content control with checkbox characters (Office 2007 & later). Content controls don't require any editing restrictions to work.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]