The 7-digit PIN/SKC (Secret Key Code)
dialog is used for Key Matching and Immobilizer 3 Adaptation.
This function is still in VCDS but is pretty much obsolete
since VW/Audi stopped giving out 7-digit SKC's in 2005. Just
in case you got your 7-digit SKC before then (along with the
necessary WSC, Importer and date the code was generated),
instructions on using this function can be found
here.
See this page for instructions for each procedure and immobilizer type:
Immobilizer Information
Important: Unless you ALREADY have the SKC
information for your vehicle and components then you will
NOT be able to do any of the Immobilizer functions.