.pdf files have one advantage - they're incredibly difficult to edit (even with the right software.) If you want to produce a document that most people can't screw with, use .pdf. Not many people have Adobe Acrobat, just Reader, so your documents are relatively safe. (Good for order forms, etc.) For things like Help Manuals, .pdf isn't necessary. If a client is stupid enough to change the html file then call and complain, it's their fault, not yours. And I'll love to get an advanced peak at the manual!