Q: Copy files using Automator but not files with the same name but different extension

I would like to use automator to copy files from my hard drive to an external hard drives that already has existing files. I would like for automator to exclude files that have the same filename but different extension. For Example, if the external hard drive has a file named filesample.doc, then the file from my internal hard drive named filesample.docx will not be copied to the external hard drive. Is there a way to do this in automator? Doing this manually will not work because i need to do this for thousands of files. I am on Mac OSX 10.11.6. I do not know scripting or automator so please be specific on what I need to do. Thank you.