A PDF (Portable Document Format) file can be opened using the free Adobe Reader application.
MP3 files are used for audio content. MP3 files can be played with most audio software such as Windows Media Player. You can also transfer MP3 files to most portable audio players.
Word files are editable word processor documents. If you don't have access to the Microsoft Word application then you can use the free Microsoft Word Viewer to open these files.
Excel documents are spreadsheets. If you don't have access to the Microsoft Excel application then you can use the free Microsoft Excel Viewer to open these files.