PDF files are everywhere. Every operating system and every device I know of can read them. They are a great way to share and publish files since they can be locked, watermarked, and viewed on pretty much any device or OS. Most office suites allow you to save files as PDF formats and there are some other great tools for creating them.
PDF Converter is a free site that allows you to convert PDF files to DOC, XLS, or PPT file formats and will also let you create PDF files from almost any file format.
It's very easy to use and there is nothing to download or install on your computer. Simply select the conversion you want to do, upload your file, enter your email address and when the service has finished your conversion, you will get an email with the link to the converted files. There is a file upload limit of 2MB, but there is no limit on how many conversions you can do.
Try it out: http://www.pdfconverter.com/free-pdf-conversion-online/
PDF - interesting infographic and lots of resources for using them