The well known MS File Transfer Manager decrypts the SDC format when files are stored online like this and the process is usually transparent. Lots of MSDNAA media is stored as SDC. ...
Should you ever want to explore the format for yourself,
a developer named imagi now offers a cmd-line tool to unpack sdc files!
get it, and more details,
here:
http://imagi.pl/
--unpacking multi part sdc files is done by copying the file parts together first.
copy /b file1.sdc + file2.sdc file3.sdc
please note,
dotnet 2.0 is required for the program to run.