In order to read PDF files on your computer, you need to download and install Acrobat Reader. You can obtain a download link from its review page from Software Informer. If you have this installed, it's possible that the file you received is corrupted. This might be the reason why you can't open it. In this case, contact the sender and ask for another version of the file.
To obtain a program that you can use to convert PDF files to DOC, use the Software Informer's database. There are plenty of software solutions that you can use in this matter.