You can use the "Special => Arbitrary Mask" on the Foramt tab.
If you need more control over the formatting and validation then you would need to use the RegExp Object.
Ok, what is the RegExp Object?
If I use the Special, Arbitary Mask, what do I put? I want to make it where the "File No" is only numeric digits with "-" i.e. 12-345-678
It is a way of writing the text or number using a special format that allows specifying not only the type of character but also values range and can be use by a number programs and services. Many higher end and programing editors have this feature as well as many programing languages. Acrobat can uses this object for keystroke checking, formatting, validating, and searching. Many HTML pages use the RgeExp for all sorts or task and validation like valid strings for credit card numbers and one can even determine the type of credit cart the number is for.