An autonumber field is used to provide a unique number in a record. It
should generally not be used for anything. If you need a number that will
be used (an invoice number, or a customer number) you should use one of the
often posted methods to locate the largest number in a table and add one to
it.
That being said, I think you could use the "format" function in a form or a
report to pad an auto-number with zeros. Try it and see.
Do a search for previous posts on this topic and you should find a ton of
posts.
Rick B