I currently have Vegas Pro 12 and looking to upgrade to Vegas Pro 18. Will I lose Vegas 12? Will I be able to go back to Vegas 12 to alter any previous projects or will Vegas 18 adopt those Vegas 12 projects? Thank you!
Newer versions of Vegas can open older projects but not the other way around. Because of that I would copy any project files you may want to edit again in 12 and add something like VP18 to the file name. However once you get comfortable with VP 18 you may never use 12 again so don't have to worry about it (I upgraded machines and didn't bother reinstall 12).
Legacy versions of VP do not have to be uninstalled or deactivated and will co-exist without issue with the newer versions. VP project <.veg> files are upward compatible as well but not the other way around. For instance, a VP-12 project file will open in VP-18 but a project saved with VP-18 will not open in VP-12.