You can simply copy the field from one document & paste it into another.
Thank you for your response. It will not allow me to simply "cut and paste" from the dropdown where I populated all the states.
Again, is there a way to duplicate the dropdown already created to use in other documents as a dropdown?
Then you should find out why it doesn't allow that. Acrobat has allowed copying a field from one PDF to another since form fields were introduced in Acrobat 3. In Acrobat DC it's best to first go into form editing mode, select the dropdown, and copy it (e.g., Ctrl+C). You can then switch to the document you want to paste the dropdown into, go into form editing mode, and paste it (e.g., Ctrl+V).