I just want to choose a nice simplified Chinese (Mandarin) font for use in documents. Adobe site doesn't make this easy. How do I shop and purchase?

Your request contains the barest information—though the same holds for the Adobe website if you don't know where to look.

Have you installed the Chinese facilities for your operating system, and are you dissatisfied with the included fonts?

Have you installed Adobe software that came bundled with CJK fonts, or are you a subscriber to the Creative Cloud and thus have access to Typekit fonts?

Modern "simplified" fonts also contain "traditional" versions of the same characters (and in fact the truly "simplified" forms are a small minority), a point I made in an old thread from 2010 that may still be worth a look for those not familiar with such issues.

If you are interested in sanserif styles, you should know that Adobe is one of the primary backers of Source Han Sans, described in several posts on Abobe's CJK Type blog.  One of its chief advantages is that Source Han Sans offers seven weights, which is unusual for CJK fonts, and can be very helpful for setting off a document's titles and sub-headings.  However, the full package is enormous and tricky to install, so you may prefer to download only the Noto Sans CJK SC version from Google (another backer), a mere 116 MB.

Good luck!

David