Document Property under Quick Parts sometimes appears grayed out or disabled in Word client and we can see that Compatibility mode written on the Word client on the top part. This happens because Word disables certain features to make our document compatible with previous versions of Office. To workaround we have to change the compatibility feature. To do that click File on the Word ribbon and select Info. Click on Convert button and click OK on the pop up message. This enables the disabled features and now we can access the Document Properties under Quick Part.
Practical notes on Microsoft 365, SharePoint Online, Entra, Azure and PowerShell - from an IT consultant who's been working with Microsoft technologies since 2004.