The folder x12a comes from the Census Bureau. I went to http://www.census.gov/srd/www/x12a/x12downv03_pc.html and downloaded "omegav03all.zip"

temp_files holds temporary files that the x12 executable creates. This folder should always be empty before running a program.

x12.ado provides the STATA interface for x12-ARIMA. To use the additive adjustment instead of the default multiplicative adjustment, use the option x11_options(mode=add).