I'm not sure I understand.
AutoCorrect has already been suggested.
AutoText would be another option. Take a look at the AutoTextList field.
AutoTextList field - How to add pop-up lists to any Word document, so you can click your way through changes in seconds
Automated Boilerplate Using Microsoft Word

It sounds as if you do not want a drop-down list but rather want context-sensitive shortcuts. If so, the AutoTextList field is about as close as Word comes.

If you want a drop-down list, there are several options available.

You might also want to look into using a custom dialog box, called a userform.
Create a Simple Userform
Create & Employ a Userform