I'm a little confused by the question, but it sounds like you're asking how to count the number of files with a particular extension in a given directory? That's not really an AI SDK question, but it's a fairly easy one to find if you google it. If you're trying to use Illustrator to do it, AI doesn't have a general purpose file API. It has a few functions to do some things that Illustrator needs, but I don't think enumerating directories is one of them.