Open the document and click on the ¶ symbol on the Ribbon's Home tab to display the document's formatting. You should now be able to see that there are two content controls, separated by a manual line break, with a paragraph break following the second one. Click on the Ribbon's Developer tab, then on 'Design Mode'. This should make the content controls even more apparent and will reveal their titles - Client and ClientDetails, respectively.

To use these controls as-is in your own document, simply copy both of them, plus the macro code to your document. To change the Client dropdown's contents, click on it, then on 'Properties' on the Developer tab. There you can add/delete/modify the entries. Pay particular attention to how the DisplayName and Value are input, especially the latter.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]