Let’s say that you have purchased a shovelware disc of Japanese fonts, such as this one from DynaComWare (discontinued, but it turns up occasionally; I bought mine at a going-out-of-business sale).
[Note that when I describe this particular disc as “shovelware”, I’m really referring to the collection of 3,000+ renamed ripoffs of Western fonts (from font pirate Bay Animation) that are thrown in; for Japanese, Chinese, and Korean fonts, DynaComWare is a legitimate foundry.]
The ripoffs (as well as the Korean, Chinese, special-effects, and kana fonts) are just stored on-disc with no protection, but the good stuff is hiding in files with the .t4_ and .t9_ extensions. The only supported way to install them is by running the included Windows program (which might not display correctly on non-Japanese versions of Windows, and of course doesn’t work at all on a Mac), but it turns out that they’re just encrypted ZIP files with a simple 8-digit numeric password, six digits of which can be inferred from the timestamp.
One thing to note is that the disc contains two sets of kanji fonts, in directories labeled JIS90 and JIS2004. The difference between the two is a subtle appearance change in a small number of characters, neatly described in this Adobe PDF file. A small number of fonts are available only in the JIS90 flavor, mostly pseudo-bitmap fonts of little real value; most people won’t notice the difference, and if you do, well, you’ve got both.
I highly recommend the disc, by the way.