Here's a sample that demonstrates probably the easiest way to do this: https://acrobat.com/#d=F3joZ1n0HIyYHm3V6MaTTg
It includes a document-level JavaScript that has a script for both the Keystroke and Format field events, which you'll see are called when you look at the Format tab of the Field Properties dialog for the field. It is possible to automate setting the script for the other fields, but it will be easiest if there is a consistent naming scheme for the fields, something like "amount1", "amount2", etc. Otherwise you have to do it manually. If you'd like more help, post again with more information about the field names you're using. If you let us know what version of Acrobat you're using, we can tell you how to get to the document level JavaScript so you can copy it to your form.
Unfortunately, the built-in routines that this example depend on don't allow for a space for the thousands separator. If you need that, it's possible, but a bit more complicated.
