Pre-fill will automatically fill in the information from the lead, they do not need to type in the first letter.
But a better solution for you would be to navigate to the forms 2.0 settings "If Known Visitor, Show Custom HTML". You can then say something like "Welcome Back" and have a download link available immediately without having them submit the form again.
A bit more info: Show Custom HTML Form for Known Leads - Marketo Docs - Product Docs
Hey Murphy - check out this article in product docs: Show Custom HTML Form for Known Leads - Marketo Docs - Product Docs
In the settings section of your Marketo form, you have an option of "If Known Show:". This section allows you to replace the form with an HTML section, when a visitor is already known.
Hope this helps!