What you are asking about is called a User Form.
Create a Simple Userform

If for any reason you can't use macros, look into the MacroButton Field. It allows you to create non-macro prompts. You can move to the next field using the F11 key.

BTW, I do use mailmerge for preparing things that go to one individual. The variable information is stored in an Excel worksheet. This is done when I have more than one document to prepare regarding the same information, sometimes over a period of time.