If the MC10000 can only stitch files in .JEF format, then what is Digitizer 10000's .JAN format used for?

Digitizer's EasyDesign program uses only JAN format. When you open a "foreign" design, or even a JEF or SEW file, that file is converted to a JAN by EasyDesign. Because a stitch file contains only colors and needle points, it does not have nearly as much information as it would contain if it were created "from scratch" as a JAN. Digitizer does its best to guess what each type of fill is, but the process is not perfect. You can save the design as a JAN file, but any missing information is still missing. Therefore when you create a design from scratch you should ALWAYS save it as JAN file, and make changes ONLY to the JAN file. If you even once open the JEF file, and then save as JAN, a lot of important detail is lost. The only way to get a "complete" JAN file that contains all information about the design is to create it yourself by digitizing your own design.

Professional designers take great pains to prevent accidental destruction of the original JAN file, by naming it differently from the files used for stitching on the machine. For example, if you were working on a boat design, you might save your original JAN file BOAT-ORG.JAN. When you save a file in JEF for stitching, you might name it BOAT.JEF. By following this convention, you won't accidentally open the JEF file and then save it out as a JAN, wiping out all of your original design.

Note that the JAN format is used only by EasyDesign. When you use the stitch editor, EasyEdit, you cannot save in any format except a stitch format, such as JEF or SEW.

Here is additional information from Janome.com. Note that these links are subject to be broken by changes made to the Janome website.

What is the difference between .sew and .jan?