Best Resource for Identifying Legit Applications?

bjb writes: While helping a somewhat computer illiterate person figure out a problem recently, they pointed out that their PDF files stopped working. Upon investigation I found something installed called "PDF Suite". Never hearing of it, I googled it with "malware" and other key words, but nothing turned up though my suspicion remained (and WOT somewhat confirmed.) So my question is where can you go to find if something is legitimate? Given the person's dial-up connection, downloading malware detection applications (and updates) is too heavy and I don't maintain a USB stick with such apps since I don't do this kind of thing often. Where can you quickly find information?