function formHandler(){
var URL = document.form.site.options[document.form.site.selectedIndex].value;
window.open(URL);
}

document.write('<form name="form">');
document.write('<select name="site" size=1>');
document.write('<option value="">Select');
document.write('<option value="docs/credit_application.pdf">Credit App');
document.write('<option value="docs/current_wa_certificates.pdf">WA Certificate');
document.write('<option value="docs/Cap_List_by_AIRCRAFT.zip">Cap. by Aircraft');
document.write('<option value="docs/Cap_List_by_ATA.zip">Cap. by ATA');
document.write('<option value="docs/Cap_List_by_PART_NUMBER.zip">Cap. by Part#');
document.write('</select>');
document.write('<br>');
document.write('<input type=button value="Go!" onClick="javascript:formHandler()">');
document.write('</form>');