🚀 go-pugleaf

If all you need is to find if the client's browser knows how to handle PDF
files, then do an advanced group search on Google Groups
(http://groups.google.com/advanced_group_search) for msg ID
7107d90c.0110150040.45dda6a1@posting.google.com (returned subject is "HOWTO:
Detect from IE web page if Acrobat/ Reader installed") to get an answer for
IE. Netscape should work the same (not tested), or you can simply examine
navigator.mimeTypes[] (I think).

What this solution does:
(1) checks if the browser knows how to handle mime type "application/pdf",
and makes the result available in JavaScript;
(2) uses standard, published, methods; nothing undocumented, hacked, etc.

What it does not:
(1) does not check for a specific application or version (the only reason I
refered to Acrobat/Reader was because this is how most people will phrase
this problem; the solution uses nothing specific to Acrobat/Reader);
(2) does not poke around the user's registry/ hard-disk/ etc.