> Has anyone designed a digital combination lock with 6 or 7 digits that
> can operate a solenoid, that the combo is user programable?

I have not myself built such a thing, though they are fairly common.  If
you don't mind my asking, what is the application?  There are a number
of things to consider when designing such locks:

[1] The possibility of an adversary trying out lots of combinations; you
    should design the lock with some sort of temportary lockout for bad
    entry attempts, but...

[2] The lock should be reasonably immune to denial-of-service attacks, and
    might possibly include an alert of such attacks.  This could be esp.
    critical in something like an exterior entry lock; an assailant who
    knew when his victim was expected could enter many bogus codes to make
    the lock "shut down", and then jump the victim while she tried to enter.
    Electrical denial-of-service attacks can also be an issue; be sure that
    all PIC inputs are well-protected (large resistors combined with caps
    and/or zeners to ground should do fine for this).

[3] If your device is to be battery-powered, you should consider that sol-
    enoids are very power-hungry.  If it's wall-powered, you may want to
    plan contingencies in case the power fails.  You may instead be better-
    served by a couple of alternative design methods:

    (1) A motor to lock/unlock the door may require much less current than
        a solenoid, though it may not actuate quite as fast.

    (2) You might want to consider using a lock/unlock pair of solenoids
        like those found in a model train "switch".  These require a fair
        amount of current, but only for a brief fraction of a second; you
        could probably use a switched coil to charge a cap and then have
        that cap feed through an SCR or somesuch into the coil.  I don't
        know offhand what size cap you'd need, though.

    (3) Electromagnets which are in contact with something can be much less
        power-hungry than solenoids.  You might consider a design where the
        door handle tries to move an electromagnet away from a striker; when
        the handle is in "resting" position, the magnet will be against the
        striker, so energizing the magnet while the handle is pulled will
        pull the striker.

    (4) If the device will be manually locked, and will not be subject to
        jarring or other such abuse, you might want to have the striker
        spring-loaded to open, but have it held closed by a permanent mag-
        net which was trying to grab an electromagnet.  Energizing that
        electromagnet with the right polarity would repel the permanent
        magnet with less current than would be required to "draw" it in.