"Metadata" includes more than document properties.
Do you simply want a list of built-in document properties?
Do you also want custom document properties? Those will not be in any list I could provide. The same is true of document variables.
https://support.microsoft.com/en-us/...word-documents

Here is a link to an old page of mine on the subject. It has not been updated for some time.
Confidentiality and MetaData in Microsoft Word Documents

You may want to look at this page Word Macros and Visual Basic for Applications (VBA) FAQ. Search for the word "properties" to see some tested code for dealing with document properties. These were written before ribbon versions but work in Word 2019.