I've toyed with several versions of TC for a number of years - but I'm really just a noob with it.
You can easily import and export drawings in/to those formats; but I beleive that
within the application (that is any drawing opened in TC) is always in TC's native
format.
To export a drawing to a different file format, just select the file format in the "save as" dialog. It's right
beneath the box where you enter your desired file name - you should see a drop-down list with a little downward
pointing black triangle - click on the triangle and the full list of formats will appear, and you can choose whatever
suits your needs.
Sorry if I haven't properly understood your question. There is an "official" IMSI/TurboCad user forum here:
http://forums.turbocad.com/index.phphope it helps,
Bill