Timestamp Macro updates date & time when Word document is edited.

I know this is Excel forum. For Excel, I have a formula I used where if the adjacent cell is altered, the timestamp is updated in the "Date" Cell.

I would like to have the same option in Word. However, if I put a timestamp in, it puts the current time, or updates the time everytime I open the document. I'm trying to have digital signature setup so whenever someone opens up the word document, and types their name in the fillable field, the date & time updates and shows when they "signed" the document, and it can be emailed back to me.

Is there a Macro that could do this? Thanks for the help!

Sorry if this is a dumb question. I added the bookmark in the area I need. Where do I place the code in Word?