boolean subtract operation between entities of different databases

 I need to do subtract operation between 2 entities existing in different databases. I am creating my dwg file, say dwg1. Now I want to load another entity from dwg2 and subtract dwg2 from dwg1.

I want to ask if I can directly use the booleanSubtract API or do I need to use firstly wblockclone initially to bring dwg2 into dwg1 and then use booleansubtract?