How to determine if a text field is numeric

There are 3 ways.

1. (Easy) - Use a Numeric field. Guaranteed numeric entry

2. (Medium) - Set a data, display, edit, and/or validation pattern on the Object Panel for the field. Any or all of these can be used to set some level of numeric compliance

3. (Difficult) - Write a validation and/or change script for the field. "change" event is called for keystrokes so you can use it to enforce data entry restrictions.

I think I misunderstood your question. I think you're looking to find the numeric parts of a Alpha/Numeric entry.

You do this with a script. This is a Core JavaScript thing, not an Acrobat or LiveCycle thing. So it's not suprising that you couldn't find it in the Adobe Documentation. It's very simple, use a Regular Expression.

Suppose that you have a field named "MyAlphaNum". A script in another field might look for a numeric part of MyAlphaNum's value like this:

// This tests for the presense of digits
var bHasNum = /\d/.test(MyAlphaNum.rawValue);

// This tests for an integer or floating Pont number
var bHasFloat = /\d+(\.\d+)?/.test(MyAlphaNum.rawValue);