PDF format is used when you need to save files that cannot be modified but still need to be easily shared and printed. In rich textual and graphical format. So converting PDF to any other format is generally not required. For converting any document to PDF can be achieved by individual software itself. e.g. MS office can export document to PDF. OR you can print any document as pdf file. OR there are online services which help converting almost any document to pdf.
For example: PDF to Word converter, PDF to Excel converter, PDF to PowerPoint converter. However, with Microsoft Office 2007 it is recommended to convert PDF to Word format as there is a new feature. If you are converting PDF to Word document in MS Office 2007 there is a new function which will convert PDF to word. I would recommend trying to use this function when you need to send your final copy of PDF to one or all of the below recipients: To any individual person (e.g. spouse, girlfriend or boyfriend) who needs to read or annotate the PDF. To a colleague or someone who has to read or annotate the PDF to be able to send it at work. For a client with whom you share your work in PDF form. To a friend or relative who has to read or annotate the PDF to be able to send it to them. If you want.