The suffix ".256" is not associated with Creo. This is a Windows Explorer folder display problem. If you tell the folder to show the filetypes you will see that all the other files have a number suffix that is hidden from you because that is the default Windows choice called "hide extensions for known file types."
You can search from inside Creo to open the file. It's a waste of time to double click on files to open Creo.
Search on the Internet for Windows File Associations for more info on why it looks like that.