Yes, projects from previous versions of Studio can be opened in Studio 14. However, once they are opened in Studio 14 they are marked as Studio 14 projects and can no longer be opened in that previous version of Studio.
When the project conversion takes place, a backup of the project is made.You can use this backup if you choose to edit in the previous Studio version for some reason.To access the backup, simply open the version of Studio that you made the original project in and import the backup file. For example, if your project is named "My Movie 1.stx" your backup will be named "My Movie 1 BACKUP.stx". The default location for these backup files is in My Documents / Pinnacle Studio / My Projects. If the version of Studio that created the project has been uninstalled and you need to open the backup in that original version, you will need to reinstall the version of Studio that created the project.
Projects from older versions of Studio such as version 10 and earlier may have issues importing properly into Studio 14 if the project is very complex.In that case it may be best to complete any projects in the Studio version which the project was created and begin any new projects in Studio 14. Another option is to output the project as an AVI or MPEG 2 file in the previous version of Studio and import that new file into a new Studio 14 project.
If after opening a project created in a previous version, you notice that it is missing 3rd party plugin effects that were previously added, please see this FAQ:
After opening a project in Studio 14 that was created in a previous version, 3rd party effects are missing from the project.