CAD files are imported through the ECTR direct integration from within the respective CAD system.
/dscsag/doc_file2doc performs a check if a original file name has already been imported. The function module checks database tables
/dscsag/cad_nbt to detect if a file has already been imported. This behaviour can be turned off by setting
plm.document.import.on.demand.knownParts.checkExistenceInSap = false and
plm.control.partnameRules.resolveInSap = false
Altneratively, you can simply import the CAD files from a different folder.