Auto Select? in Drop Down List Box help

I am trying to create an invoice template and added a drop down list box in the description field to provide valid available product description to select from to avoid typing.
Problem that I am having is that this only allows me to select description by scrolling down in the list box. I would like to be able to type first couple of letters and have the cursor move down to the correct section to make selection quicker and easier specially since I will have approx 500 different description to pick from....

Would greatly appreciate any assistance with this request.