Here is documentation regarding the available tag types and the different options you can add that are specific to Adobe Sign.
Use double brackets in Word and those fields will be converted to form fields.
Double brackets are not necessary when adding form fields in Adobe Acrobat Reader, just use the text inside the brackets as the title of the form field.
The tags are mostly useful for text fields. It is not necessary to use special dropdown tags in Acrobat Reader, just use a dropdown field. The options work and are still useful for non-text fields (i.e. :signer1)
In order to get fields to populate into a form, the steps are different for each field type. For the remainder of this page, form field title refers to the form field title up to "_es_". For example, if a form field is called "Form_es_:signer1:date", the title is just "Form"