Partly through the aid of Help Desk WebRatio, partly after several attempts, here is the solution: insert the following script before the Create. I hope this can be useful.
#input String filePath
import com.webratio.rtx.RTXBLOBData
import com.webratio.rtx.blob.BLOBData
import com.webratio.rtx.blob.ExternalBLOBData
import com.webratio.rtx.blob.ByteArrayBLOBData
import org.apache.commons.lang.StringUtils
import java.io.File
def path = StringUtils.substringBeforeLast(filePath, "\\")
def fileName = StringUtils.substringAfterLast(filePath, "\\")
def ext = StringUtils.substringAfterLast(filePath, ".")
File inputFile = new File(path, fileName);
RTXBLOBData blobFile = new ExternalBLOBData(fileName, inputFile, rtx);
return blobFile