This radio button controls whether you want your pledge reminders to default in the form of a letter or a form.
Form
When you record a pledge and are deciding whether to remind the person with a form or a letter, a value of Form is the default.
Letter
When you record a pledge and are deciding whether to remind the person with a form or a letter, a value of Letter is the default. If this is selected, then a valid letter code is required when all pledge gifts are entered.