I actually haven't bought the software, but that link looks fine to me and seems to be the family of sellers that others have used.

And for your 2003 you shouldn't need the 16 to 20 pin adapter, that was only on early E53's (1999-2001 I believe)

good luck!

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards