These are sequential save files. Every time you save, a new file is created. So, you can go back an find an older version of the file when needed, by deleting all the more recent ones (or moving to another folder). Most of us have a *.bat file or some other mechanism to "purge" the older files periodically (as well as all the other crap that clutters your working directory, such as trail files, logs, error reports, circular reference reports, mass property reports, etc.). If you work in a PDM system, you won't deal with these directly.
I suggest you get out of the habit of opening files in Creo by double clicking them in Windows. Use the "Open" function within the program instead, and set up favorites or "common folders" as needed so you don't have to navigate your directory structure each time.
You can eliminate this behavior with the config.pro option "save_file_iterations no", but this is not recommended, as the ability to go back in time with those older versions can be a big help at times. Presumably, your old Creo 3 setup had that setting in effect, but your new one doesn't. I'd leave it alone, and just get used to opening via the program, and purging regularly, such at the end of each workday, or workweek.
(I'd give you the code for my purge *.bat file, but I worry one aspect of it may be proprietary; I wasn't the original author. I've seen similar ones posted here in the past, and on other forums; perhaps someone else will chime in. This has been necessary part of the Pro/E experience for a long time.)
