How do I back up Quicken data file to a disc?

If you're using a DVD as your long-term storage or backup, just be sure that you always have an external DVD drive available should you need to access that information. Since Macs produced in the past 8-10 years have not had DVD drives, and aren't likely to in the future, you'll definitely need an external DVD drive in the future to access that information.

Also, be aware that while DVDs are great for storing a lot of data, they are not foolproof. A DVD that works fine today may have problems in 10-15 years. I went through a project at work, where we had a lot of arched photos on dozens of DVDs, and when we needed to restore data from them more than a decade later, some had read errors that ranged from minor to catastrophic. We had duplicate sets of the DVDs, and in some cases both duplicates of a disc failed. In theory, writable DVD drives should last at least 25 years; I'm just telling you that if it's critical data, you might want to duplicate it somewhere else as well.

Copy the backup file from the DVD back to the Mac using the Finder before trying to open it. After moving it to the Mac, double click it and Quicken will open and confirm you want to restore the backup.