Zamzar is a free online file conversion tool that allows you to convert Document, Image, Music and Video Formats without having to download any software. For example, you can convert a PDF document to a .doc file, or you can convert an MP3 file to a .wav file with this online tool. There are literally hundreds of different conversions supported. See a list here.
Zamzar also has the ability to convert files from URLs with support for a variety of video sites, including YouTube.
The interface is super easy to use. Once you have uploaded your file to be converted, you supply an email address to which Zamzar will send your converted file. You are then given 24 hours in which to download the file. Keep in mind, there is a 100 MB limit in place for each file. The site indicates there can be up to a one hour delay between submitting your file and getting back the converted file. I did a test conversion with a larger PDF file and had my conversion back in about 20 minutes.