Or, Myra ... once you have the file created, just rename the extension to something like LOK (for locked). This won't actually not allow Illustrator to open the file (it'll open any file created by it), BUT, you won't ever see it in the OPEN menu of Illustrator, nor will it be associated with Illustrator so it'll not open in Illustrator that way either. Unless the other parties know this trick, and that's to click on FILE, OPEN, then in the filename box type in *.*, Open, then they won't be able to SEE and thus open the file. If you type in *.*, then ALL files in that directory will show, including the one with the .lok extension. Just double click it and it'll open just fine in your Illustrator. I just used ".lok" as an example. You can use any extension (or no extension) and you'll get the same results. For special files, I often use .ai7, .ai8, or .ai9 to distinguish what version .ai file they are, or even apply an abbreviated client name fo some files.
Bob