I have no idea what you mean. For example, pressing F8 has nothing to do with making a dropdown selection. If you want to make a dropdown selection, click on the dropdown. Nothing could be simpler and you certainly don't need a shortcut - unless you're trying to avoid using the mouse - but even then a shortcut won't make the selection for you.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

I will try to explain me better:

Everyday i write documents talking about people and every time i talk about someone i need to put his name and number. So i'm trying to avoid writing the name and searching his number.
The purpose of using a shortcut it's to simplify the work: everytime i need to mention someone i will press F8 adding the Dropdown and choosing the correct name.

Ex:

The joao n.º123456 it working good for now. the paulo n.º324543 is missing the sessions. the jorge n.º235631 is wroking harder to complish the session.

Hope i've clarified you