yes, you can format the field for display purposes, but...
generally speaking, it's not a good idea to use an autonumber for a field
that users are going to see/use. for instance, formatting 1 to show as 001
will only work until you reach 1000 records, then the formatting has no
effect.
also, an autonumber keeps a hard sequence. once a specific number is
assigned to a record, it will not be used again, even if the record is
deleted. so you may end up with "gaps" in the number sequence in your table
records.
and keep in mind that an autonumber field just keeps going and going - to 2
billion+ and then negative 2 billion+ (according to another answer to a
posted question along these same lines).
suggest you review your need for a 3 digit number and consider an
alternative to using the autonumber field.
hth