The most likely reason for being unable to open a file is that you do not have a program for handling that particular file type. This is an example of why it pays to have the display of file extensions enabled. The file extension will tell you what kind of file you are dealing with. As the figure shows, Windows offers to find some software for you and that may be the way you want to handle it. Personally, I would prefer not to rely on the choices that Microsoft makes. I would go look up the extension myself to see what kind of software is involved (for example, at the links in this post). However, that is a fair amount of work if you are also going to have to research some new software just to open the attachment.

You can save yourself some time and aggravation if you prepare in advance for some of the most common types of file that give average PC users trouble. Here are the problem situations that I have seen most:

• Your correspondent uses Microsoft Word; you don’t and can’t open DOC files. The solution is to download a free viewer from Microsoft now and save future annoyance. DOC files are very common and you will keep getting them. Or get Open Office. Unfortunately, Wordpad no longer reads DOC files.
• Your correspondent has the entire Microsoft Office and you don’t. You only have Word. She sends you an Excel spreadsheet (extension XLS). In fact, the sending of Excel files to others without realizing that they need software to open them is quite common. Again, the solution is to download the free viewer from Microsoft or a program like Open Office now and be prepared once and for all.
• You have an older version of Office and someone sends you the new file format DOCX or XLSX from Office 2007. Older versions of Office won’t open these new XML formats. Get the converters here.
• Someone sends you a picture in a file format that won’t open. How do you know it’s a picture? You did enable file extensions, didn’t you? The problem of incompatible picture formats affects mostly older systems but new or old your system will benefit from installing a program like the freeware IrfanView and its plugins. You will then be prepared to handle almost any graphics format.
• You get a multimedia file that won’t play. There are a number of possible problems with audio and video files but lacking the correct codecs is the most common. Codecs are a subject outside the scope of this article so I will just say downloading additional codecs may solve your problem. Consult the information for whatever media player you use. Another common problem is that there are incompatible file formats; Windows Media Player won’t open RealPlayer or QuickTime files. You need to install players for these formats. Again, the file extension will identify what format a file is in.
• Your correspondent has an Apple Mac and sends you files in a Mac format that Windows doesn’t recognize. Checking the file extension will tell you if a Mac format is involved. Ask your correspondent to try another format.

Finally, it is less common but another possible reason that a file won’t open is that, although you have the proper software, your file associations are wrong. This can happen from installing and uninstalling a program that took over associations or from other causes. You can read more about file associations here.