CAD files are imported through the ECTR direct integration from within the respective CAD system.
Function module /dscsag/doc_file2doc performs a check if a original file name has already been imported. The function module checks database tables /dscsag/doc_red (field masterfilename_l) and /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
in default.txt.
Altneratively, you can simply import the CAD files from a different folder.