Vehicles Euro standard 6 and alternatively fuelled vehicles need this sticker:
Yes, there is a national scheme with differently coloured stickers from 1st January 2015. Currently it is only required in Vienna, Niederösterreich and Oberösterreich. The stickers can be purchased from garages in Austria and cost 2,50 €, see here for more details.
They are also distributed at certain repair garages and some ÖAMTC offices, see here for a list of garages.
A) a copy of the vehicle registration documents.
B) the CEMT document or other document or datasheet that states the emission class of the vehicle.
This is the documents were the emission class is documented. It can also be a link /printout with weblink to the eg UK (or German or Italian etc) database that states what Euro class that vehicle registration vehicle.
C) Your VAT-number.
The price of each sticker is € 20,- excl. taxes and mailing costs. An invoice will be sent with the stickers, that should then be paid by bank transfer to DEKRA.
Delivery time: 5 business days.
The email should be in English or German. The vehicle and Emissions standard documents can be in any language.