Quite a lot has been changed since v.12. Especially about the menus.

If it is from evolution to PRO for the same version there should be no problem.

Your question can only be answered with a : "give it a try", if it is from v.12 to the newest version. If the old project uses the left menu system in the v.12 then it could give trouble.

If it is from v.12 to the newest version, I suggest you use all material from the old project (images and texts) and then start a new  project in the new version. Doing it this way you will have a "clean" project, and it could be faster than use a lot of time to correct errors from a conversion, and you could have a lot of "garbage" from the old project.

ESTEFANIA, the short answer is yes. You can go from evo to pro (but you can not go from pro back to evo). You simply need to go to step 5, export project and create an iwzip of your existing project. In the pro version, select import and browse to the iwzip file. As John said in his post, how the latest version of WX5 handles a project generated in V12 can produce unexpected results.