Except for the fact what you want can't be done with a documents saved as a PDF, there is nothing to stop the MACROBUTTON method described in the link working in a document that contains formfields. Simply insert Section breaks either side of where you want the picture(s) to go and leave that Section of the document unprotected. The process will work best, too, if you save the document in the older .doc format.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]