how to add a drop down list ?

[Vass]

I have a template, In a "text box" on the right is the note 'special
instructions'. I want a drop down list to appear when the template is first
opened, so the author can select the appropriate instruction from the list
for insertion into the document.

The instruction are:-

by fax
By email
subject to contract
without prejudice
Without prejudice save as to costs
And a blank field where any details can be entered

Any guidance please would be appreciated, many thanks