Dynamic Stamp with Popup Selection and automatic addition of some Text depending on Selection

hi folks,

i customized a dynamic stamp (template) for approving pdf documents. you can choose the approvers name from a popup menu and the stamp shows his name. it works fine, but i want to add another textfield which should contain the signature of the approver. i already built a specific font with all necessary signatures. So what i need is an extra textfield to be populated with a single character ("a", "b" or "c") based on the selection the user made in the popup menu. If user selects the first name of popup menu, the extra text field should be populated with a simple "a" (in my font "a" is the signature of the first name in popup menu); if second name is selected, the extra text field should be populated with a simple "b", and so on...

Do you guys have any idea how to do this in javascript ?