It's probably happened to you before that you download or receive a file and it has no extension at all, or something rather obscure which can't be correct. Here's a selection of 5 tools to help you identify files which have none or the wrong extension.
You can use https://www.filetypeadvisor.com/ to recognize the format of your downloaded file. Simply upload the file and we will test it and show you the results.
download a fit software to open the file or requse the file sender to send you a file which you can open