PW_Workdir come frome ProjectWise
From Userposting:
"You can attach reference files (in the new version) as
PW_WORKDIR:dms000xx\name.dgn and if that file has already been copied out
all of the set logic will still happen like you would want it to happen, and
you'd still be working nicely with Projectwise. The PW_WORKDIR config
variable is a new addition to our integration that is really just a
shorthand for your working directory base. "