When we upgraded 4.5 to 6 styel docuemnts we used an export/import method.
Build an export workflow to copy the records to an identical file cabinet then export them back to the old file cabinet...
The system converts the files when importing to the new file cabinet, Copying them back just moves them back into play.
It is slow but it is a work around we still use....converted a 4.5 just a few months ago....